When we had our house built in 2003, we had a terrible time with field mice getting into the garage.
I tried those glue traps (a horrible invention...especially when the mice don't die and are out there screaming) and the old-fashioned spring-loaded kind...but a little gruesome, too...
But, man, these electric mice zappers are awesome and work! The couple of mice I had to get rid of were drawn into them within hours and the 4-AA batteries killed them instantly. (Peanut butter seems to be irresistible to them.)
You may want to leave out outside the camper for a while...I'm betting you'll get quite a few!
Rat Zapper Classic Electronic Rat Trap-RZC001 at The Home Depot