I have had experience with that spray foam and it isn't waterproof. It will hold moisture in there big time.
I am going to put a new floor in our 88 and doubt I will own it long enough to see that rot out seeing as she has over 300K on it now.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
Mike has a good point on the electrolosis problem but there is one old timer's trick that seems to work quite well on seams and sandwich sections. Get a bucket of roofing tar - that black, nasty gooey stuff. Coat both sides of the "sandwich" liberally so that you squeeze out the excess as you bolt/rivet the sections together. If there are seams and crevices, turn a heat gun or some such (I don't recommend an open flame ) on the pieces to get the tar to flow. Once the aromatics boil off that tar, it remains elastic and the original application penetrates rust and cavities. It may not be as good as POR 15 at converting rust, but it even works to seal repairs in water tanks - like the bottom of evaporative coolers - for years at a time. The stuff is cheap, so use plenty. An uncle of mine used roofing tar as a sealer in his body shop on the Gulf Coast and swore it filled and worked better than anything else in the salt spray. It's messy, so get a gallon of mineral spirits to clean up with - fair warning.
Best be careful you don't get nabbed by the Wreck Check Squad!
A couple summers ago I was driving thru TO on a hot august day and all of a sudden my passenger side mirror vanished. Dam, glue let go and the mirror just dropped away.
When I bought my '02TJ I had it undercoated. The undercoating I had seen in the past was just an oilspray...but this stuff turned out to look something like that "blow-in" newspaper insullation mixed with tar.
It's been a few years and it's still on there....of course I haven't hit any big rocks while rock crawling.
I don't know if this stuff can be re-coated...or if they have to peal it all off and redo it. But for sure, if it will trap moisture if there's a hole in it.
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