The belly has been pretty well sealed and no rodents inside this spring after the trailers winter's sleep. Ours has the furnace cold air return in the stair risers. I used some aluminum screening on the back side just in case a rodent somehow found another missed open door in that belly cover. Nary a mouse poo now. Aluminum screening in much less edible then the fiberglass.
The pin box was a haven for birds on the current and the previous 5er. I made up a removable wood panel that covers the gap. using rare earth magnets epoxied on it to hold in place with the pigtail coiled and inside the gap. It took some time fitting and adjusting but does the job well
Dave W along with my DW, Susan and our poodlepups, Callie & Molly,2011
Ford F250 6.7 CCLB, 5er Hitch Option w/B&W Hitch,,Ride Rite air bags, 2014
Montana High Country 343RL (38')w/disc brakes