working on it wrote:Why not use spray on automotive undercoating? Also in rattle cans, also at Tractor Supply. I'm using it on my TTT. I've also used it for many years on various vehicles, that have been exposed to many more miles thru worse conditions than a TTT or TD will probably (or should be) exposed to. An occasional inspection and/or touch up is all you'll ever need. And, you can always have a spray can handy to do so, when on the road.
I used the black asphalt emulsion on my floor (underneath) when I built the TD in 2006. It dried fairly quickly & wasn't a great problem for me to clean up (don't understand what all the objections are about)? I also added 1" 'blueboard' insulation after coating with the black stuff. Used construction adhesive & plain wood 'batten's to hold the insulation in place. Thru more'n 12K miles over all kinds of roads/terrain Never had any problem with road debris causing any damage to either the 'coating' or the insulation. In 2010 I was rear ended while on a short trip. Trailer was damaged but useable. After returning home & following the insurance settlement I repaired the damage myself. In the places where the impact had 'splintered' some of the floor joists you could see where the emulsion had penetrated approx 1/16" or so & the wood (spruce) behind the coating was still like new. No moisture had ever penetrated it. The collision did open up a couple of seams on the wheel wells inside the cabin which allowed water to enter. After discovering this & drying it out thoroughly, I sealed the seams inside with caulk & CPES. Underneath I used the 'rattle can' of automotive undercoating since it was much easier than 'painting on' the emulsion again (upside down). The aerosol undercoating appears to have done a good job sealing. I don't expect any problems, seeing how long the original emulsion has lasted to now but, I carry a can of the spray-on undercoating for 'just-in-case'.
Some of the damage to my TD showing the emulsion coating & splintered floor joists


After using the spray-on undercoating on the open seam
