Before baby, I didn't mind the hot, horrible, sticky interior of a vehicle on a summer's day here in Charleston. Not as much as I do now, anyway.
Seriously. It wouldn't be half as bad if my Jeep had magical rear-blowing vents. Instead, the vents are positioned to blow directly on the back of Lizzie's rear-facing carseat. Not especially effective.
So in an effort to save some time, I decided to fight back. I filled up an empty jug of OJ, froze it, and have been using it this week when I run errands. I grab Lizzie. I put my frozen baby OJ jug in the car seat. I return, and at least the car seat isn't hot enough to melt faces. It's not perfect, but it saves a lot of time. I'm okay sweating for a few minutes but I wasn't a fan of getting a sweaty-haired baby out of the vehicle.
I don't mind the condensation too much. I suppose if I were going to be gone for hours and hours it might be a problem but we haven't had that issue so far. If you try it, let me know how it works for you!