Spray Foam on Frame Rails

I want to do something similar. Specifically what did you buy/where did you get the spray foam? Is it a kit?
WhatI did was drop the coroplast completly. Removed all of the fiberglass insulation, secure all of the wiring, and install rigid insulation (polyisocronate) 1" thick = R6.5. I put as many layers in as would fit. The inside of the frame has two layers. Some areas of the floor have six layers. Last, I reinstalled the coroplast in sections no longer than 6'. Now when I need to go in there for some reason, it is almost as easy as lifting the hood on my truck.... And the rigid insulation can be easily removed when needed. The extra insulation takes a lot of time to custom cut it around things, but it is VERY noticeable when the mercury drops. The main problem with doing spray is it is permanent. And if it doesn't turn out well, you pretty much stuck with it..... Kind of like laying concrete... I pay a pro for such work, as a do over is NOT easy,
Be sure to wear a GOOD dust mask when removing the fiberglass insulation and wear old long sleeved clothes and gloves. That stuff is nasty.
 
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That's got to help a bit on the huge heat / cold sink.

Does the spray foam stick good enough to not let moisture behind it?

I was thinking the same thing Orbiker. Years ago, some buddies and I took a trip in a Class A that had foam sprayed on the fuel tank. At the first fuel stop while filling the tank we noticed a huge fuel leak from the tank. Turns out the foam captured moisture between the tank and the foam and rusted the tank out. We removed as much as the remaining foam as possible to try and patch it but the tank had to be replaced. Also, the auto industry used to sell undercoating as a dealer installed item, but many times that lead to premature frame rusting as well. That said... I know the RV frame is much thicker than a fuel tank but I thought it was a good question.
 
The foam I used is a closed cell foam that will not let moisture penetrate it, but it is always possible to have a spot that didn't bond well and get moisture behind it. So far, I don't think it is an issue.
 
Update to this thread, foam has been doing well, no real issues. I had some freeze up issues Christmas of 2023 and temps weren't horrible, maybe -5F. I found that the heat pad for the fresh water tank had stopped working. I dropped the coroplast and inspected everything and what I found disappoints me. For starters, under the drain area of the fresh water tank, the reflective foil barrier was folded out of the way instead of going under the drain portion of the fresh water tank, same for the fiberglass batting in the same area, so basically no insulation under the drain area of the fresh water tank. This allowed the bottom of the freshwater tank to basicly freeze solid! Next I inspected the batt insulation above the rest of the coroplast and what I found was lack of quality control! Over half of the fiberglass batting was short of reaching frame rail to frame rail by 6-8 inches. This basically defeats the purpose of having insulation in the belly and explains why I poured lots of extra heat into the belly and still had freeze ups. I removed all of the batt insulation behind the fresh water tank and reinstalled it correctly. I used a bead of expanding foam between the bottom of the rear most crossmember on the frame and the rear wall to seal off the 3/4 inch gap. Then I ran a full piece of fiberglass insulation up against the rear most crossmember to provide insulation to the rear most section of the belly. Then I cut 12-16 inch long sections of fiberglass to add to the oem batting to make sure it covered frame rail to frame rail. I strung sections of duct tape tied to the crossmember behind the fresh water tank to the rear bumper to hold up the fiberglass batting until the coroplast could be reinstalled. I ordered a Ultra Heat tank heater rated for 75 gallons and it is about double the size of the factory pad. It is also about 160 watts compared to 77 watts for the factory pad. I had to use a heat gun to warm up the glue on the pad as well as the bottom of the water tank because it was only about 20 degrees out when I installed the pad. I unfolded the reflective foil and notched it to fit under and around the fresh water drain and did the same with the fiberglass under water tank. I also used some eterna bond tape to seal the area above the spare tire and also where the coroplast was notched at the rear of the frame. When this latest cold snap breaks, I will take the Solitude out and see how it does, but with temps in the last week at 27 -36 below zero, I will stick to keeping the wood stove cranked up in the house.
 
Thanks for a very detailed account of your efforts to winterize your coach. There have been quite a few threads on this subject recently. It is excellent to see the results of real-world experience.
 
Thanks for a very detailed account of your efforts to winterize your coach. There have been quite a few threads on this subject recently. It is excellent to see the results of real-world experience.

The biggest thing I have learned is to never assume your RV was built exactly the way it should have been.
 
Our Imagine owners manual states the RV is not designed for use in freezing or sub freezing temperatures without additional modifications.
We are fair weather campers so not a problem for us. Been in low 40s with no issues.
Rich
 

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