One thing I do for my 1967 MGB is put down a moisture barrier. I have an asphalt garage floor. Get some plastic sheeting and roll it out on the floor. Your can duct tape the corners so the wind won't blow it around when you open the door. This creates a vapor barrier of sorts. It also prevents the MG from "marking its spot" with oil drips! It can't hurt to do the same for the Boxster. As previously mentioned, dryer sheets do work well to keep away rodents. I drive my car during the winter, but not when there is a lot of salt on the roads. When you plug in the battery tender, run the plug wire out of the front trunk by the windshield, then close the trunk. I hate winter.
