I’m interested in bolstering the insulation of my travel trailer… preparing it for 4 season camping. The walls and ceiling are fine - I just need additional insulation under the floor. The holding tanks are suspended beneath the floor in the void between the frame members. There is wiring, water lines, and gas lines traced thru this space. whatever is used will be exposed to the elements from below- spray from the road, high wind… etc. I’m entertaining a couple of options…1) After all of my modifications (running a few more wires and plumbing - spraying a thick layer of foam up onto the underside of the floor encapsulating all of the wiring/plumbing. A drawback of this method is that Jayco depends on maintaining a cavity thru which warm air is circulated (although inefficiently) to warm the floor and the plumbing in the void space. A 1/4” membrane called coroplast forms the lower barrier to weather - this is screwed to the frame… not an airtight seal!2) The other option is to use 1” foam board placed in the void - leaving a 2 - 4” space above anchored with screws appropriately and spray a thinner coat of foam to seal the space…leaving the void above to allow air to circulate.Which method do you recommend? - which foam product will best stand up to this environment? Do I need to coat the foam to protect it? If so what type of paint/coating is best?The holding tanks hang well down into the void - approx. level with the bottom of the I beam frame… currently the coroplast lies snuggly against the tanks - I plan to put heating pads on the bottom of the tanks. Can I spray foam directly onto these pads - Maybe 1” thick?.

You probably do not want to heat the spray on foam insulation, it probably is not designed to be over say 90F with heat applied (well I guess it can sit outside in the sun though).I would recommend reflex insulation under the tanks. It can be applied directly to the heating pads on the tanks (with contact cement) then the coroplast onto the reflex. You should be able to glue the reflex to the Coroplast if you like, and then it will have the 1/2" or more air space for most effective insulating properties. The key to superinsulating the basement is not really how many R-value you will have, but how airtight it will become. Keeping in the warm air is the KEY. Seal all the joints with good aluminum duct tape (the type with a pull off backer is really strong). Good luck,Fred.Good luck,Fred.

Do you have a Jayco with the coroplast now? I owned a 19RD Jayco TT with the coroplast. Of all the complaints I had with Jayco I think the coroplast was somthing they did almost right. My Jayco had large voids or openings into the coroplast. Basically poor job of installation. I closed and sealed all those openings. I used foam and sheet metal in large openings, foaming the underside of sheetmetal before installing. My black water valve was enclosed. My grey water valve was not enclosed. The grey water valve was the only problem in cold weather. All that said, if I was going to enclose an underbelly I would want both valves enclosed. Seems like that wouldn't take much modification. Put heat pads on the tank. Run some furnace heat in the area. Use the coroplast and make sure all was sealed. The coroplast works. It was Jayco's sloppy assembly line installation. I never had problems down to about 5 degrees except for exposed grey water valve. We would dump water in toilet instead of in grey water tank. I sold the Jayco for other reasons. Jayco had some good ideas using the coroplast. JMHO.

Yes, I have the coroplast now - and you are right, there are several large gaps in the fit and finish. And it is just inserted above the flange of the I beam frame... lots of air leakage. I could just run a small bead of foam insulation around the edge! And yes, my black tank, fresh water tank, and one grey tank and valves are all enclosed - I have the rear kitchen and a galley tank located at the rear of the trailer has the drain line exposed for 2/3rd's of the length of the trailer. Maybe I should place a valve at the tank before it exits the heated space...Thanks for the ideas.

Not to be Debbie Downer but nothing you do to the underside of your trailer is going to drastically change your life in terms of heat retention. You're talking about single % gains in anything you do. The only exception is if you plan to keep the trailer in the same spot and want to build skirting around it with insulated walls. And even that won't be drastic.The fundamental problem with TT is the thin walls/roof and the relatively small amount of cubic feet inside. There just isn't enough space to hold much heat for long. The air exchange is just too quick. I've often joked that my RV is the only place I can be too cold and too warm at the same time :)On Edit: I guess I should add that it also depends on where you are talking about the 4 seasons. Canada is certainly a lot different than Arizona.

I'm more concerned with keeping the plumbing from freezing... I can crank up the heat, use heated blankets, or wear more clothes to keep me warm

Insulating the Belly of my TT | Good Sam Community

14 Replies

mtofell1
Explorer
Oct 20, 2015
Not to be Debbie Downer but nothing you do to the underside of your trailer is going to drastically change your life in terms of heat retention. You're talking about single % gains in anything you do. The only exception is if you plan to keep the trailer in the same spot and want to build skirting around it with insulated walls. And even that won't be drastic.

The fundamental problem with TT is the thin walls/roof and the relatively small amount of cubic feet inside. There just isn't enough space to hold much heat for long. The air exchange is just too quick. I've often joked that my RV is the only place I can be too cold and too warm at the same time :)

On Edit: I guess I should add that it also depends on where you are talking about the 4 seasons. Canada is certainly a lot different than Arizona.
Jframpey
Explorer
Oct 20, 2015
Yes, I have the coroplast now - and you are right, there are several large gaps in the fit and finish. And it is just inserted above the flange of the I beam frame... lots of air leakage. I could just run a small bead of foam insulation around the edge! And yes, my black tank, fresh water tank, and one grey tank and valves are all enclosed - I have the rear kitchen and a galley tank located at the rear of the trailer has the drain line exposed for 2/3rd's of the length of the trailer. Maybe I should place a valve at the tank before it exits the heated space...

Thanks for the ideas.
WyoTraveler
Explorer
Oct 20, 2015
Do you have a Jayco with the coroplast now? I owned a 19RD Jayco TT with the coroplast. Of all the complaints I had with Jayco I think the coroplast was somthing they did almost right. My Jayco had large voids or openings into the coroplast. Basically poor job of installation. I closed and sealed all those openings. I used foam and sheet metal in large openings, foaming the underside of sheetmetal before installing. My black water valve was enclosed. My grey water valve was not enclosed. The grey water valve was the only problem in cold weather. All that said, if I was going to enclose an underbelly I would want both valves enclosed. Seems like that wouldn't take much modification. Put heat pads on the tank. Run some furnace heat in the area. Use the coroplast and make sure all was sealed. The coroplast works. It was Jayco's sloppy assembly line installation. I never had problems down to about 5 degrees except for exposed grey water valve. We would dump water in toilet instead of in grey water tank. I sold the Jayco for other reasons. Jayco had some good ideas using the coroplast. JMHO.
Golden_HVAC
Explorer
Oct 20, 2015
You probably do not want to heat the spray on foam insulation, it probably is not designed to be over say 90F with heat applied (well I guess it can sit outside in the sun though).

I would recommend reflex insulation under the tanks. It can be applied directly to the heating pads on the tanks (with contact cement) then the coroplast onto the reflex. You should be able to glue the reflex to the Coroplast if you like, and then it will have the 1/2" or more air space for most effective insulating properties.

The key to superinsulating the basement is not really how many R-value you will have, but how airtight it will become. Keeping in the warm air is the KEY. Seal all the joints with good aluminum duct tape (the type with a pull off backer is really strong).

Good luck,

Fred.

Good luck,

Fred.

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Insulating the Belly of my TT

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