Joseph,
My experience with field mice and house mice is that once you have a mouse invasion, you have a recurring mouse invasion problem. The little varmints leave their scent (read pee) all along their path. This odour marks the trail for the next mouse. Unless you block up the trail, mice will continue to follow the path. Perhaps some odour blocker would work but short of scrubbing with some strong cleaner I wouldn't bet on it. BTW poisons are a bad idea. Other than the risk to pets who hunt mice, if the mouse dies inside your vehicle walls/ducts, you have real trouble.
On our '86 Syncro Westfalia, I found that the air intakes are not properly covered with screening. If you remove the black plastic headlight shroud you can get at this possible invasion point.
Larry

Joseph Roy wrote:

Has anyone found a effective way of keeping mice out of their Westy? I have an '84 Westphalia, water cooled, that seems to draw mice as soon as I park in a campground. Food is always tightly secured, yet the mice come in through the dash and run around inside all night. They climb up the tires, next I see them coming down from the dash area. Recently, I stayed up and set traps. By morning I had a pile of 15 mice. Does anyone know if 12 v. ultra-sonic pest repelling devices are available? I've tried to caulk as many holes in the dash as I can reach. All suggestions are welcome. Thanks.