I have a 2003 22' International and had some subfloor rot in the back and I thought I would share some insight as I have just completed this project.
The subfloor projects under the inner shell into a channel which is what holds the shell to the chassis and floor. In order to replace a large section of subfloor you have to remove all the floor cabinets, bath and any other items that this floor is sitting on. You may also have to remove items that are on the good part of the floor because you cannot remove the required items because these item are in the way.
On my 2003 with the rear bath and kitchen you cannot remove the countertop without first removing either the bath or the refrigerator. I removed the 4 piece fiberglass shower / toilet combintation as the floor was rotten under the bath as well.
Once you have everthing removed you have to either remove all the rivets in the lower inner skin and remove it or you can remove most but the the top layer and tie the skins up our of your way. You have to get access in between the inner skin and outer skin to replace the bolts that go from the top side of the channel through the subfloor and through the bottom of the channel.
Once you have all this remove you pull as much rotten floor out as you can. There will probably be a black layer of tarp like material between the subfloor and metal frame. Go ahead and cut this up and get it out of your way. Trying to save this is way more trouble than its worth. Did as much rotten wood out of the channel as you can and if possible just use a angle grinder to cut through the bolts and remove from the the top and bottom.
Airstream does this neat thing with the bolt to keep them from working loose and they bend the bolt over as a locking mechanism. No way to remove bolt without just cutting through it in the channel. Be careful not to cut beyond the bolts. There will also be some screws in the channel screwed into the subfloor from the top. Remove this or cut them off as well.
Once you have all your subfloor and bolts / screws removed carefully run your finger in the channel to make sure it is clear. You will feel the backside of some rivets holding the channel which is normal. Do remove these rivets. If your Airstream has a rear bumper assembly like mine (holds the sewer lines and receiver hitch) did this was probably the source of the water that ruined your floor. In order to remove this aluminum trim strip on the outside you will have to pull the decorative rubber strip off of the aluminum to access the 3 rivets on each side along with about 12 screws holding this on. On my unit this was a large u-shaped trim strip that wrapped around the bottom of the airstream and sat right above the rear bumper.
Once removed is showed the Airstream had not sealed the area where the shell sits on top of the bumper assembly
. This allows any water that collects on the rear bumper to flow directly into the subfloor assembly. This was caulked with Sikaflex sealant.
To replace the subfloor you will need to either use the old subfloor as a template for the curved floor or you will need to build templates. I built templates out of paper and cardboard using the Tick-Sticking method (google it). Once you templates are built test fit them. Staple your template to your new plywood and then trace around it and cut out the rounded edges with a jigsaw. You should be able to flip the template you built for side and use it for the other side and it is a mirror image.
Once you have your sections of replacement subfloor cut use a spar urethane on the bottom, edges and top. Several coats are recommended especially on the edges. This will keep any water or moisture from penetrating the new flooring.
In my case in replacing the entire rear section of subfloor I had to build it in 3 sections. Two large sections for each side and filler section in the middle. You will have to drive the new subfloor into the channel in the rear first and then drive it towards the sides until it reaches fully into the channel. You will then screw and glue support boards on the inside edges of these sections so your filler board will have something to rest on and screw to.
Once you have all the subfloor in place you will use self tapping screws to screw it down the frame and use bolts and screws in the channel. I used 1/4" bolts with nylock nuts so they cannot come loose in the channel. I used #14 (1/4") 1 7/16" long wafer head bolts (ordered through fastenal) to screw the subfloor directly to the metal frame. These are self-drilling and the wafer head is large to pull the floor down nice and secure.
It doesn't take a large amount of these screws (maybe just 3 or 4 across each chassis metal beam). You want to cut back far enough so that your joint is on one of these beams so the floor is fully supported.
Once you have all your channel bolts, channel screws and subfloor screws in place you can re-rivet your lower inner skin back in place. Make sure you use aluminum rivets. You can use bondo or wood filler to smooth out and imperfections in the subfloor before you put down your finished floor. We are using all vinyl planks but you could use a single sheet vinyl as well. I personally would shy away from any type of floating floor or laminate. Floating floor can get moisture under them and it it cannot breathe you will get mold growth.
I would recommend full glue down flooring. Many people have had great success with floating floor and that is fine, I just don't trust those locking seams under all the twisting and flexing that a trailer undergoes.
Once your new floor is down you can replace all the cabinets and other items and your good to go. This is much simplified version of all the steps. I'm very mechanical and I can tell you Airstream does not design these to come apart easily. The rear bath bath was a complete pain in the ass and you have to be really careful not to break any of the fiberglass.
The biggest lesson I have learned is if you can afford to take it to the factory to have it done then do so. I am a serious DIY'er and this project has been HUGE! I would rate this job a 8 out of 10 on a technical standpoint and it really sucks this had to be done because of lack of sealant on the rear bumper. The reason I wrote this is because you see a lot of info on the older vintage airstreams but not a lot on new models.
Take lots of before pictures and videos. Put all your hardware in plastic bags with where the go written on the bags. This was also a good time for me to replace the old 110 toilet with a 310 and I also fixed some of the fabric headliner that was sagging.
One thing leads to another on a project like this. I would guess I will have at least 100 to 150 hours in this project when done so its not for the faint of heart.
If your Airstream has a rear bumper you really need to check for the presence of sealant behind the trim strip. The floor in my 2003 was OSB and it just turned to soggy sawdust because of this design flaw or worker missing the sealant during assembly. It has many documented cases online of this sealant missing so remove the strip and check. Use Sikaflex 221 to caulk this seam or equivalent. Do not use silicone as it will not stick to the aluminum and will fail over time.
The Sikaflex 221 Aluminum color works well for all the caulked joints around the windows and other fixtures. It stays flexible in extreme temps and sticks to the metal like the dickens.
If you ever get stuck on something message me and I can hopefully talk you through it. It has been a learning experience to say the least. Peace Out!