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Old 03-17-2016, 05:08 PM   #1
2 Rivet Member
Opelika , Alabama
Join Date: May 2015
Posts: 23
Insulating subfloor catch-22

I'm replacing the subfloor and the bellypan and I've run into a conundrum. If I install the bellypan first, I can't install the bolts from the outriggers through the subfloor because I won't be able to get to the underside of the bolt. And if I install the floor first, I won't be able to insulate under the subfloor unless I pick up the hole trailer so someone can walk underneath it to install insulation. How have people handled this issue? Ideally, I'd like to have a well-secured bellypan, a good quality insulation under the subfloor, and a subfloor that slides into the c-channel at the base of the skin.

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Old 03-17-2016, 05:19 PM   #2
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1960 33' Custom
Saskatoon , Saskatchewan
Join Date: Jun 2005
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There's plenty of threads with people who have insulated with styrofoam SM or similar just glued or installed with screws and washers


1960 Sovereign 33' Pacific Railroad Custom
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Old 03-17-2016, 05:39 PM   #3
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1964 22' Safari
1962 28' Ambassador
enosburg , Vermont
Join Date: Aug 2007
Posts: 313
Any I've seen the fiberglass insulation was layed on the frame and the floor bolted over it. No doubt that has / do'es contribute to frame rust. With body on frame you can jack and crib block it, gives you a couple feet to work, but on your back. Body off frame you can flip the frame over as needed. Much easier to do a new belly pan. Something to consider, I didn't insulate the floor in the last one. Just the waste tanks, pipes and heat duct. Can't see any disadvantage.
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Old 03-17-2016, 06:05 PM   #4
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1989 32' Excella
Sharon Springs , New York
Join Date: Jan 2016
Posts: 90
A real simple solution is to put throw rugs on the floor since heat rises anyway. If you really think it, that little bit of insulation under your TT is going to help much, your kidding yourself. Focus on insulating the water-pipes and sealing any drafts to keep out the cold and leaks to keep out the dampness. The nice thing about rugs is that if they get wet you can dry them and you won't have to worry about wet insulation rusting your frame. If you are concerned about moisture seeping in through the tires, park on poly/rubber mats, they'll create a moisture barrier for your unit. Been RVing for 30+ years in some really "drafty" RVs and cold floors is usually a very small worry compared to other things. I wouldn't stress it too much, good luck...
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Old 03-17-2016, 06:09 PM   #5
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Opelika , Alabama
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Posts: 23
Thanks a ton guys.
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Old 03-20-2016, 08:26 AM   #6
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1991 34' Limited
2013 23' FB Flying Cloud
Conroe , Texas
Join Date: Jul 2012
Posts: 186
I filled all of my floor cavities with a large clear plastic sheet from Home Depot making sure I filled all the voids between the frame members.
The plastic laid across all the frame beans and I pushed it down allowing it to sink and fill all the cavities. This would allow me to add my fiberglass insulation. The plastic sheet held the R-13 fiberglass in place for any work I needed to do underneath. I installed my new pressure treated plywood floor decking.
Then your still able to do any work from underneath since your looking up at clear plastic and pink insulation.
Poke a couple of small drain holes in the plastic in each void or between frame members to allow any future water that may collect to have a way to escape.
You never know what can happen.
Hope this helped not sure what your particular problem is.
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Old 03-20-2016, 10:05 AM   #7
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1972 31' Sovereign
Lexington , Minnesota
Join Date: Feb 2009
Posts: 3,382
We did not insulate under the floor. We, instead, put a floating cork floor in, which has great insulating power. We are summer campers, anyway, in our climate. The fiberglass remnants we took out were pretty trashed and full of mouse nests. Mice love fiberglass insulation!

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Old 03-20-2016, 11:54 AM   #8
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1994 34' Excella
Warren , Manitoba
Join Date: Apr 2006
Posts: 396
If you use the pink or white fiberglass insulation, once it gets wet, most of the insulation properties are gone. If you want to use the "bat" type of insulation, I recomend a mineral type such as Roxul. It will dry and retain all of the insulation properties. Do remember that any type of bat insulation geetting wet will take a long time to dry and mould will have a great place to start. JMHO!! Chris

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2002 Chev 2500 HD Duramax
1976 31' Gone but fondly remembered
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