Sealing Holes from "varmints" too
I spent a good part of a day plugging and sealing EVERY hole, oversized grommet, and any other seam or crack that mice, etc could get into my 2014 Flagstaff Emerald Edition 27RWLS trailer when it was new.
I was always told that any hole bigger then a nickel was an invitation for "chewed wiring" in this part of the country.
I used closed cellulose black landscape foam as well as electrical "duct seal" and made rubber seals that sealed the gear driven slide shaft against the frame when it was opened or closed as well as the shaft for manually opening that slide.
The "under belly" covering had areas that were not fully sealed and were addressed also..... especially were the rear trim under the rear bumper met the under belly covering around the frame ends.
I actually used some left over aluminum flashing from a residential skylight installation that happened to be the same color as the lower trim to fit in the frame ends. Looks like it came from the factory with the ends sealed off.
This is my second winter and after looking around in hidden spaces, so far no signs of "Creature Features".