Steve Kimock, who was very involved with Mike Bendinelli with his gear, said that you shouldn't let your equipment be anywhere you wouldn't be comfortable. Speakers absorb moisture and electronics degrade from corrosion. As a builder of guitars and amps, I've seen many examples of instruments that were left in cars, etc. Amps aren't as obvious, but there is a toll taken when moisture gets into electronics, etc. I usually come home from a gig, take a short rest and maybe a snack, then get the stuff out of the van, even though I'm dead tired. I love what my gear does for me and I'm willing to return the favor. I guess it's up to the individual and how much energy they'll put into keeping their equipment in optimum condition. It'd be interesting to read the moisture level in a vehicle in a garage, just to see if it's actually dry enough. I only have a carport, so I don't leave anything out.