Give 'em somewhere else they'd rather be. Put a 5-gallon plastic bucket close to the truck with a gallon of water and about a pound of cracked corn in it. Lean a board up against the lip of the bucket with a couple of inches hanging over the rim. As the corn ferments, the mice (and rats, if any) will climb the board and dive in, trying to get to the corn. It's a one-way trip, because they can't climb the slippery sides of the bucket.
My friends who brew white lightning have a terrible time keeping the varmints out of their mash vats. After a couple of days, they bloat and float, and they can skim the carcasses off the top. It doesn't seem to affect the taste of the finished product, thank goodness!
Jerry
