Positive cabin pressure will help if it's not too cold outside. Put a small fan in a window furthest away from the smell. Seal any gaps with cardboard or rolled up towels. Ideally the smell backtracks to the hole the mouse climbed in. Or at least vents the smell outside until it dries up and stops smelling.
I have a dead mouse in my ceiling. Read that slivers of Irish Spring keeps mammals away. Some say spiders too but I read it's only mammals like mice.
If your trailer sits you can leave mouse traps set on the frame rails with no bait. Inside the trailer set the traps along walls in lower cabinets.
Get a flashlight and check your onboard generator if equipped. Look for nest material. If you have compressed air spray behind the genny and watch for nest material to come floating out.