Thanks for the suggestions! I did manage to find a large, unscreened opening in the area where the shore power cord is stored. I opened the rear access door, and felt around in there - there is a large hole cut in the rear wall, in line with the false wall of the bathroom.
I usually leave the small, streetside power cord access door open after pulling out the power cord, so I'm figuring the power cord makes for a pretty good mouse highway into the TM. I guess I better start keeping it closed!!!
I'm not sure if there is a way to screen up that opening in rear wall. There's not enough room back there to attach a piece of screen, and the hole is too large for foam. Might be a good place to keep some peppermint soaked cotton balls though...
Thanks again...
Mike-