I didn't quit like the clip on fans in the Auto parts stores. So I looked around.
I found an almost perfect size portable fan.
O2cool 10 inch fan, $30 at bed bath and beyond (use that pesky 20% off coupon they send every other week!!), $25 at Amazon. It takes 6 D cells, last about 40 hrs, also comes with AC adapter which can be connected to a cigarette 12 volt to 110 v converter.
It fits pretty snug in the side pockets of the trunk, the fan is sitting on top of the Tesla bag which holds all my adapters.
Hope this helps with all the owners with the jump seats !!