Dicor vs ProFlexRV for Underbelly Repairs

[OBSPowerstroke]

I'm getting ready to seal up my newly built Coroplast underbelly for the fresh water tank and was planning on using black ProFlexRV sealant until I noticed it specifically stated not to use it on EPDM or hard foam insulation. Since I used an EPDM rubber canopy gasket on the new Coroplast underbelly, I thought black Dicor non-sag sealant might be a better option.

Whatever sealant I go with, I also plan on using some of it to seal up a few areas on the underbelly where propane and water lines go up through the floor. This means the sealant will be in contact with the Darco underbelly tarp in some areas, which is also a plastic that may not be compatible with ProFlexRV.

Another option is to not worry about running sealant around the Coroplast underbelly even though the dealer sealed it up completely with a black caulking/sealant of some sort shortly after I bought the trailer. The EPDM rubber gasket I used on the rebuild seals it up pretty good as it is, and I know water will find it's way in there from road spray, and I'm worried if I seal it all the way up, there will be no way for the water to run back out or evaporate; creating a bigger problem. The underbelly was soaked and the fiberglass batt insulation was trashed when I tore it out for the rebuild, and this was likely due to the drive home in the pouring rain from getting the frame cracks fixed by a shop.

Any thoughts? Should I go with the Dicor or ProFlex or just skip it altogether?

Thanks!

[Community Alumni]

Why not use expanding foam? That's how trailers come from the factory. Just run a line down the edges and join the underbelly with the bottom of the trailer. The foam will expand to give you a seal, fill any irregularities, and it's waterproof. It would be much cheaper than tubes of caulking.

[OBSPowerstroke]

DiskDoctr wrote:
That looks very nice!

Keep in mind that foil insulation works differently than regular insulation. I can't tell if you had some insulation on the old stuff, or if you are talking about removing batts of insulation?

This topic comes us often in certain heating and cooling discussions on other boards as people try to improve their sticks-n-bricks.

It all depends on what you're trying to accomplish 😉

Thanks! Yeah, I realize the foil insulation functions differently than regular insulation, and that, by itself, it does not add much, if any R-value. My intent with using it for this install is that it will hold in what heat is piped into the enclosure from the furnace as well as the heat lost through the floor to theoretically keep the fresh water tank from freezing.

I figure the foil stuff has to be better than the soaking wet fiberglass batt insulation previously in there that was squished flat between the bottom of the tank and the Coroplast, and the insulating properties of the foil won't be compromised by the inevitable water that finds its way into the underbelly.

[DiskDoctr]

That looks very nice!

Keep in mind that foil insulation works differently than regular insulation. I can't tell if you had some insulation on the old stuff, or if you are talking about removing batts of insulation?

This topic comes us often in certain heating and cooling discussions on other boards as people try to improve their sticks-n-bricks.

It all depends on what you're trying to accomplish 😉

[Mortimer_Brewst]

When I needed Coroplast for our "former" trailer I found that prices varied wildly. It pays to call around. I ended up getting it for $15 per 4 x 8 sheet. I added some 2 x 3's between the I-beams in order to give me something to attach the Coroplast. Stainless steel screws and fender washers worked great. Overlap joints so they won't catch air as you go down the road. Small gaps can be filled with foam sealant. While it was opened up I glued some foam board to the decking for added insulation.

[OBSPowerstroke]

BillyW wrote:
I added my own coroplast to the underbelly of my trailer over 10 years ago. I did not seal anything, and purposely left a low spot to the rear for water drainage, just in case. It has stayed pretty clean inside and is reasonably easy to access if necessary. I made sure there were no big gaps, but otherwise left it alone.

Thanks for the advice. I'm leaning towards not sealing it up all the way and only filling a couple of the larger gaps where the Coroplast is cut to fit around the rear spring shackles on each side with landscape expanding foam (this was how the factory or the dealer addressed the original gaps). When I fabbed up the new underbelly, I used the old one as a template, and wish I hadn't matched the cutouts for the shackles on the old one, as I could have made much more precise cuts and not even needed the foam this time around.

I'm pretty sure my old underbelly was retaining a lot of water, as the metal on one of the corners that the Coroplast was mounted to was really rusty, as was the bolt in that location. I'm guessing that was the low point and water built up there and slowly drained out the threads of the bolt. The good news is there was no sign of mold or water damage on the floor above it.

path1 wrote:
After I had a water hose clamp break free, I also was wondering what to use. Never really could decide. Made what I thought was a good temp fix with black gorilla tape. Also replaced insulation matting with foam board insulation. If another leak happens, foam board doesn't fall apart. And added to annual check inspection to tight or check hose clamps on my annual inspection.

3 years later gorilla tape still working good and still wondering what would work best.

(side note) Also at the time of repair, couldn't find any full size corroblast sheets at any RV store. Ended up getting a big white sheet from a sign shop. Last year at a border patrol check point they asked lots of questions about big white patch job. This summer I think I'll spray paint it black, so it matches rest of underbelly. I do admit a big white patch job looks mighty suspicious.

Glad to hear your temp fix of Gorilla tape has held up for over three years, as I used that stuff to patch up areas of the Darco that melted due to the heat generated when repairing and reinforcing the frame. I may run a bead of sealant around the tape for good measure.

I had a hard time finding a full sheet of black Corplast as well. I went to the local RV dealer and asked about it, and they looked at me like I was speaking in tongues. I was able to find a sign shop close to work that had a few black sheets laying around and even was able to get them to cut the basic dimensions. I paid more than I should have, but it saved me a 40 mile round trip out to the airport and back during rush hour to get it from a plastic supply house. If I couldn't find any black sheets, my plan was also to spray paint a white sheet as a last resort. I also replaced the batt insulation with foil bubble wrap.

I have a week long trip planned the beginning of next month, so I think I'll run the trailer without the underbelly further sealed up and inspect it when I get home. I'm sure we'll be driving through plenty of rain, so I'll have a good chance to test it out and see if I want to seal it up all the way.

Here's a pic showing the old vs new underbelly:



Thanks guys!

[path1]

After I had a water hose clamp break free, I also was wondering what to use. Never really could decide. Made what I thought was a good temp fix with black gorilla tape. Also replaced insulation matting with foam board insulation. If another leak happens, foam board doesn't fall apart. And added to annual check inspection to tight or check hose clamps on my annual inspection.

3 years later gorilla tape still working good and still wondering what would work best.

(side note) Also at the time of repair, couldn't find any full size corroblast sheets at any RV store. Ended up getting a big white sheet from a sign shop. Last year at a border patrol check point they asked lots of questions about big white patch job. This summer I think I'll spray paint it black, so it matches rest of underbelly. I do admit a big white patch job looks mighty suspicious.

[TurnThePage]

I added my own coroplast to the underbelly of my trailer over 10 years ago. I did not seal anything, and purposely left a low spot to the rear for water drainage, just in case. It has stayed pretty clean inside and is reasonably easy to access if necessary. I made sure there were no big gaps, but otherwise left it alone.