Rodents (mice) keep infesting trailer and pickup truck ???

I'd try to make sure to fix any places they have been getting into to trailer. Then placing the large plastic outdoor rodent bait boxes under the truck and trailer. If they can feed outside before trying to get in the trailer they should die outside and not inside stinking up the trailer. Make sure not to store any food inside the trailer and wipe down and clean the microwave, stove, stove hood (including the filter if it has one), counter tops, sinks and cabinets where food has left any residue between uses.