Michigan for me is a six month a year state for driving 914's. I'll be driving again in the spring.
Once car is in a Car Bag, carbag.com, has no fan, uses a desiccant and zips up but I don't particularly care for it. Found that some critter ate into my bag this summer and made a nest in the folds, luckily they did not do this during the winter season!
I bought another Car Capsule, carcapsule.com, the most recent iteration has a battery charger with its own battery that will keep the thing inflated for 40 hours if there is a power outage. It's much thicker than the originals that I have and has a seamless bubble with a checkerboard floor. Fancy.
I highly recommend the Car Capsule. In my mind, it's "critter evident" rather than "critter proof." I had a problem with one of the chargers and Phil, the owner, was gracious about making sure the problem was fixed and that I was happy. Excellent product, excellent service, perfectly preserved cars...what more could I ask for?
Anyway, I once read that cars kept on a trickle charge have less corrosion overall?
One of the cars is sold to a buddy this spring. Four is too many!
Paul