My wet gear gave my last car terminal rust, and that was trying to minimise that effect. Leaving wet gear in the car at work all day etc (no choice). But, had window down, but still not good enough. This rust was the biggest issue.
With my van, I made sure I insulated. I used EVA foam and ply wood. Works a treat. See pic below. When I'm at work with gear in the car, I leave the rear and sides open, and hope people are not immature enough to steel something that is worth nothing to them.