Not sure how you'd hook a portable AC unit up - if it involves wiring, you absolutely are not allowed to do it, as it would be a vehicle modification.
Some "beat the heat" tips:
1. A towel on the seat makes a huge difference
2. Place a piece of old carpet on the floor - that sucker gets really hot on the feet!
3. You can buy a cool gel pad for the seat - (likewise, for winter in Ohio, I have a heat pad that slips into the microwave - really helps to keep my legs & butt warm, but that's another post)
4. Use a gel neck wrap - google "cool gel neck tube"
5. Finally, when it gets near 100 here - we've been known to throw a bag of ice on the dash behind the wonderful cooling fan - ha - try it, it actually works!
