I'm starting to get serious about adding insulation under my TT, especially under my tanks. (We had our first water line freeze recently, while camping in 11 degree weather.) I am planning to use styrofoam board for insulation, with Coroplast underneath to hold it all in and protect it. I will use self-tapping sheet metal screws, with washers, to fasten the Coroplast to the frame. (By the way, does that sound about right??) So I went onto the Home Depot site, and they have many different thicknesses of Coroplast, from 0.157 inches to 0.393 inches. Usually, I would opt for the thickest one -- bigger is better, right? But are there pros and cons that I am not seeing? For example, are the thicker pieces more brittle or more prone to sagging?Thanks in advance for your input!

well, the thinner ones is the one most TT mfg use. I'd guess our outback is about 1/8".I would think 1/2" would be stiffer and less sag, but much harder to work with. the 1/8" stuff can easily be cut with a razor blade and rolled up.And Idon't think the thick stuff would add much insulation. I'd go for the thinner stuff and foamboard above it.

When I worked on our trailer last year I found that the cheapest place to buy Coroplast was from a sign shop. Prices varied widely, but I was able to get it for about $15 for a 4 x 8 sheet of black Coroplast. The thickness was 1/8". I glued foamboard to the decking above for insulation. I also had to add some crosspieces to have something to screw the Coroplast to. I used 1"x3" lumber for this.

Under my trailer it looks to be about 1/4". Just an estimate. I didn't measure it.

Mortimer, thanks for all of those tips! It never would have occurred to me to contact a sign shop. What did you use to glue the foamboard to the decking?

When I added 1/8" coroplast under my tanks, I ended up needing to run a strip of angle aluminum to support it in the middle.

What thickness of Coroplast for enclosing TT underside?

ktmrfs
Explorer II
Nov 22, 2015
well, the thinner ones is the one most TT mfg use. I'd guess our outback is about 1/8".

I would think 1/2" would be stiffer and less sag, but much harder to work with. the 1/8" stuff can easily be cut with a razor blade and rolled up.

And Idon't think the thick stuff would add much insulation. I'd go for the thinner stuff and foamboard above it.
Mortimer_Brewst
Explorer II
Nov 22, 2015
When I worked on our trailer last year I found that the cheapest place to buy Coroplast was from a sign shop. Prices varied widely, but I was able to get it for about $15 for a 4 x 8 sheet of black Coroplast. The thickness was 1/8". I glued foamboard to the decking above for insulation. I also had to add some crosspieces to have something to screw the Coroplast to. I used 1"x3" lumber for this.
hohenwald48
Explorer
Nov 22, 2015
Under my trailer it looks to be about 1/4". Just an estimate. I didn't measure it.
profdant139
Explorer II
Nov 22, 2015
Mortimer, thanks for all of those tips! It never would have occurred to me to contact a sign shop. What did you use to glue the foamboard to the decking?
TurnThePage
Explorer
Nov 22, 2015
When I added 1/8" coroplast under my tanks, I ended up needing to run a strip of angle aluminum to support it in the middle.
bobndot
Explorer II
Nov 22, 2015
Do you have a heat duct down there ? or heat pads on the tanks ?
Maybe wrap electrical heat tape to the dump valves ? When it gets down to 11F or the single temps, you might need a little more help than an underbelly cover that's insulated.

I have a heat duct heating my underbelly with a covered belly and no insulation . I would not want to use it below 25F.
I would foam it, add pads to the tanks and wrap the valves as well as any exposed lines. If you choose to use boards, tape the joints for a tight seal.
Remember in order to make underbelly repairs down the road, all that work will need to be removed.

Here is more underbelly insulation ideas.

https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/28616062/srt/pa/pging/1/page/1.cfm
Jay_Pat
Explorer
Nov 22, 2015
I have not dropped/opened up under the trailer.
I have some kind of support/cross members for support to screw into.
My coroplast is held in place by self tapping screws.
You will have to cut around suspension and anything else already mounted on the frame.
I would consider taking measurements of where important items are in case you need access to them. Then you will know where to cut a hole.
Pat
westend
Explorer
Nov 22, 2015
You are probably using "styrofoam", generically, like "Kleenex".

My suggestion would be to use extruded foam board or polyisocyanurate instead of expanded foam board (Styrofoam). Both of those have more durability and higher R-value than expanded foam.

Since the chloroplast is only a shield and they all have the same properties, I'd opt for a thinner one.
profdant139
Explorer II
Nov 22, 2015
Again, thanks to everyone for these tips. And westend, you are right that I was using the term generically, but I did not know there was a difference between extruded foam and expanded foam -- I will look carefully when shopping. I am hoping that the products at Home Depot or Lowes are clearly marked so that I can tell the difference.
chr_
Explorer
Nov 23, 2015
profdant139 wrote:
Mortimer, thanks for all of those tips! It never would have occurred to me to contact a sign shop. What did you use to glue the foamboard to the decking?

Sign shops are great for stuff like this. I needed two sheets of aluma core to close up some wall openings s in a clean room we bought some equipment out of. It would have cost me $1K to ship a few sheets from the supplier, but a fast signs in Syracuse had it and the franchise owner was happy to sell it to me.

They also had 5' x 9' sheets, which is what I used. Saved me from bonding two together. Large stuff is just sitting on the shelves.