get the garage door roller shutters. not the big open one.

Then keep your car OUTSIDE the garrage and build a fake wall behind the garage door ( inside ) and insulate the room as much as possible.

You will then find that your temps are better and you can use the whole garage as a reptile room.

Or corner off a section of the garage and build fake walls around it and get an exaust fan to keep the air going in and out.

Surely someone will tell you more on this.