I used moth balls for years, took a week or so to clear out the smell come spring but not nearly as bad as you make it out to be. No mice in the 8 winters I had the hybrid. As you don't want this route, you can put down a few of the sticky mouse traps, a bait or 2, drier sheets can't hurt, and make sure there are NO ways for the mice to get in from below. I used spray foam for the few little holes I found.
We completely emptied the trailer, including the bedding cushions. Bump up the tire pressure 10-15%, remove all the batteries from the detectors and such. Make sure the 12v batteries are fully charged, fluid filled, and disconnected. Clean the outside, check the roof caulking, fold down the radio antenna. Close it up and install a pail or 2 of DampRid.
Having the trailer at home I could hookup the trickle charger a couple times over the winter, if you leave the batteries on the trailer and live in the north, you need to keep them fully charged.
Happy Motoring
Bob & Deb
W Ma.
12 F150 HD SCAB EcoBoost LB 4x4
14 Escape 5.0 TA