I use decon poison... we had the same problem with our farm equipment/trucks, and it was the only way to successfully control them when there seems to be an endless supply moving in and causing damage.
sprinkle a few pellets of the decon around the engine compartment and place a packet or two inside the coach... after eating the decon, they leave the coach to find water and never come back.
equally as satisfying is the fact that while they are in residence, they have something to eat other than the wiring...
after trying to plug the holes they make with steel wool or silicone, only to have the varmits chew thru another area, the decon is the most effective remedy that we have found for long term use with the very least amount of effort...