I'm feeling your pain, but only you can get this fixed, big job but have faith. For that floor I'd get a few cans of that foam insulation, get some string/ tie wire, anything run between the rails underneath the trailer to temporarily support the foam as it hardens, and most importantly a tyvex suit gloves and face mask cause that shit is sticky and you're going get it all over. Maybe even start with some of the hard foam board 1-2" as mentioned for your main level.