In the post above, two up, you can see that some of the cross frame members have a 1/2" strip of plywood above them. This is where the joint in the floor panels occurs. I elected to put in solid foam insulation, which required an adjustment for that 1/2" step.
I started by press fitting 1-1/2" thick foam into the webs of the main frame members (see photo in previous post). This provided a nice solid wall to end-butt the large horizontal pieces of foam.
The first horizontal layer was 1/2" thick and fit precisely between the edge of the plywood step and the next cross frame member. Below that I press fit in a piece of 1-1/2" foam, cut to fit the entire space between the cross frames and from main frame to main frame (some were pieced together). All surfaces were coated with liquid nails. In addition, 3" deck screws and 3/8" thick particle board washers were used to retain the foam. This allowed the deck screws to have 5/8" purchase into the plywood above. You can make the washers with a hole saw with the guide bit removed (the guide bit hole is too big to retain the head of the deck screw--gotta put that hole in later).
After all that, I injected space-filling foam along the edges and into any gaps. This serves two purposes. First, zero air infiltration. (Necessary? probably not.) Second, this stuff is great glue and I want those pieces of foam to stay put [forever]. You can just see a little of the space filling foam oozing out along the left edge in this photo. You can also see that I used cable mounts to firmly attach the brake wires to the wooden frame members--I always worry about them bouncing around and fraying.
What's the down side? All this stuff is waterproof and now pretty much air tight. A liquid spill that soaks the floor or finds it's way under the floor is going to be trouble--very long time to dry. I guess it's a tradeoff. Ask me in 5-10 years.
I put an extra layer of 1-1/2" foam under the back access area. There are lots of pipes back there that make me crazy when the outside temperature goes below 25 or so. I want all the protection possible for that space. By the way, the belly pan is 5" deep, so you can put a lot of insulation in there. But it's probably wise to keep it out of contact with the belly skin, since this area isn't sealed and you can expect some water to get in a run around on the skin.
You can't see it in these photos, but the POR 15 has been overcoated with Rustoleum Metalic Brite Finish--no name, but the cap is a sparkly aluminium. I did not use the POR primer, since the cure has only been going for three days. I did sand the heck out of it to get the bugs down from something like 60 grit to more like 120. Hey, the bumper and frame aren't a 57 Chevy, OK?
Next post will be the belly skins and we find out if my hole-finding technique flies!
Great to see your solutions to insulation. Several of us have tried our own idea to insulation solution. It's raised many questions and lead to lots of discussion. We have decided to get together in 30+/- years. We will then take our trailers apart and compare the results. Some of us will be 95 years old or so. Should be an interesting event. You are invited. By the way spending many hours under, on top of, or in an Airstream has no affect on ones mind.
Generally speaking, spray on foam insulation "should not" be used in an Airstream or Argosy trailer.
The principal of construction used by Airstream is called "semi-monocoque", which means a load bearing shell, just like an aircraft.
Therefore since the shell is load bearing, the "shell and frame" twist as you travel. That twisting will cause the spray on foam to slowly but surely, disintegrate into chucks and small granules or powder.
Also when the spray on foam cracks, moisture will be trapped resulting in rust forming on the chassis.
Stay with an insulation that breathes and you will be fine.
Many years ago, Airstream tried the foam on the frame. Results in time were 100 percent negative.
. I'll let you know how long it takes to wear off (yes, I tried the olive oil without any perceptible improvement).
It takes about a week of washing, and general use of your hands to wear it down to go away. I did the bottom of a car and you are 110% right, no matter how well you prep, it gets on you.
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A friend of mine who is a professional painter smears cold cream on all exposed skin before he starts a messy job . It all comes off in the shower. I tried it once when I did a particularly messy spay job and it worked great.
Generally speaking, spray on foam insulation "should not" be used in an Airstream or Argosy trailer. ...twisting will cause the spray on foam to slowly but surely, disintegrate into chucks and small granules or powder.
Stay with an insulation that breathes and you will be fine.
Andy
Well, I guess the experiment continues...
Andy, thanks for pointing this out. I'll have to watch for trouble over the next few seasons. I'm hoping the disintegration won't happen, since my sprayed in foam is only about 1/8" thick.
It's been 5 days and the POR is slowly coming off. I'll pass on the grinder method.
Now, few comments about replacing the belly skin with two panels. I elected to use the full 4' width on the curb side and a 14-1/2" strip on the street side, riveted together lengthways after the two sheets were otherwise secured. The difficult part is finding the existing rivet holes in the frame. I made a handful of "hole finders" by bending small pieces of aluminum and drilling a hole through both sides, then inserting a #10 screw in one side. The screw fits perfectly, but the threads often hung up as I tried to remove them. It would have been better to use 3/16" pop rivets with the stem removed, due to their smooth shaft. You'll find you need various sizes--the length from fold to hole, since there is little clearance with other frame members onthe street side (in this 1971 Caravel), so variations of 1/16" are needed. And thank goodness for Klingons (you know what I mean).
Alll I need to do now is finish off the bumper locker. I elected to use a separate piece of sheet aluminum for the locker bottom (the cross frame will be sheathed, too).
... only two weeks into a 4-hour job, and I finally got the axle installed , with a little help. Two floor jacks are optimum--it's possible that you could do it with one and a small emergency jack. The axle slipped in easily, but you do have to wrestle with the fact that it wants to rotate due to the drum being out on the swing arm. I had to attach a makeshift "come along" (the yellow strap) to move the axle slightly once it was in the pocket. The rear bracket holes aligned perfectly. The front slot in the bracket was too far forward by 5/16", or so (see photo). It was simple to drill out to fit. One other note about the fit--the top of the axle bracket fits snugly up against the web of the main frame, which is 1-1/8" above the top of the cutout.
The shock bracket turned out OK, too. I could have mounted it another 3/4" outboard, but it will work fine on these mounts--the clearance between the upper shock body and the frame will be minimal, which is why I should have mounted the lower bracket (on the swing arm) further outboard. The shocks are at their max extension when the wheel is off the ground. Sorry, the mounts are hard to see due to the jack being in the background.
Recall that I shortened the axle by 3/4", or 3/8" on each side. My visual inspection today tells me that I still have more clearance on the inboard side of the wheel than outboard. But the reall gain is that the drum is 3" lower when weight is off the axle. Together, this makes removal and installation of the tire a snap--previously it had to be forced between the drum and wheel well skin. Now there is easily 3/4" clearance. What a difference!!
The U-shaped pice of aluminum has a hole drilled through both sides, so the holes match up. The screw (better, a rivet without its stem) acts as a locator pin. You slide the device over the edge of your new piece of skin, then "guess" about where the hole in the frame is. After you futz around a little, the screw goes into the existing hole (that you can't see, because it would have been covered by the skin--this assumes the skin is already in position and you're trying to locate an existing hole under that new skin). With these small tools, the hole has to be near the edge. There are commercial tools that look like long bar-b-q tongs that allow you to do the same thing 18" or so from the edge.
Once the screw is in the hole, you now can use a punch to mark the proper location of where the hole should be in the skin, since the visible piece of the tool has a hole in it that is precisely ove the location of the screw, and hence over the location of the existing hole in the frame.
I did about 40 holes this way and most were dead on--two had about 2 mm error. Sometimes you don't get the screw all the way down so the tool is flat again the frame (hangs on a thread or something), or the U-shape can be "leaned" a little, resulting in a bad mark. All-in-all, they worked pretty well.
By the way, is there a need for old but servicable drums/brake parts? The old axle is going to the dump in a few hours unless I hear otherwise.
There will be at least two more axles coming off this year, maybe four, all early 70s vintage. I'd like get an idea if there are crippled trailers out there because these drums are obsolescent. Anyone know?
I don't think it's worth it to save 70s brake parts--perhaps there's an occasional exception. A whole brake plate is about $50, which would have modern magnets.
I do not have a use for the drums. However in the auto industry good old brake drums are a prize. In the RV industry there are a lot of generic parts so one could just buy a loaded brake assy and install. Still I think the drums would be of some value to someone if you have the space to store.
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Phoenix ~ Yeah it's hot however it's a dry heat!
I think you need to keep them for six months. I kept mine, and within a month someone on the forums put out a call for the parts. I sent him the whole box for the cost of shipping.
Included the allegedly 'very valuable' threaded hub caps.
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Axis Axle is installed!! 
One other note about the fit--the top of the axle bracket fits snugly up against the web of the main frame, which is 1-1/8" above the top of the cutout.
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