Did you have pack rats or mice? I am not used to mice being a big problem here in AZ. I would use plenty of traps and make sure you are storing in a really clean area away from vegetation. Dry cement or plaster of paris mixed with corn meal or flour will kill the critters once it hardens inside them but is not a poison that will go up the food chain.
We are in covered storage that is surrounded by blacktop. The heat from the blacktop does a good job of keeping the critters away.
Zack and Donna plus Millie and Ranger
"Life is too short to stay indoors, enjoy the ride!"