My first thought was if you are using a cooler in the first place, why the heck are you keeping them in bags for the trip???
Why not just go the next step and convert the cooler into a portable frag tank?
Get a converter for the car so you can plug in equipment, add filtration, heater if needed.
it would be brain-dead easy to plumb the cooler if needed, you can silicone/glue racks into it to keep the coral stable in transit, etc., etc.
Honestly, why not convert the cooler into a "nano tank", I can't imagine it would be that difficult, only getting enough power while driving may be an issue, but I doubt it.
Then you may even have more "personal" time with the girlfriend, and that's always a good thing.