So far so good using this foam from Home Depot.
I used 2 or 3 cans under the TT! I foamed EVERY OPENING, the entire slot along the frame, went around 2x. Don't forget, if you have an under carriage spare, lower it and care for the 1" opening for the cable that drops down the spare tire. I used a 4x4 blank plastic electrical box cover, cut a slot for the cable, 4 self tapper screws into the under-belly then foamed the slot, and a small hole for the cable to freely slide up and down. Mostly overlooked access point.
Don
My Registry
RVing with SOLAR