heat and O2 is going to be your main factor. you'll have to get a dc to ac power converter then get a small pump with an air stone for the O2. as for the heat it's hard to get a converter that can handle that kind of amperage. I think that a chemical heating source will work for 6 hours. like the palm warmers you get for those cold days out in the elements.
I agree with Sisterlimonpot, you need some kind of air pump going to keep the water oxygenated and also something to keep the temp. regulated. Sisterlimonpot had a good idea about using the "hand warmers" for heat, I would just make sure I double bagged them in some ziplocks so none of the chemical in the "hand warmers" would leak out in your water. Also if you cant come up with one of those dc to ac power converters to stick in your cig. lighter, you can get a battery air pump at your LFS, I think they last about 8 hours. We have had a few storms here where the power goes out for a few hours, they have saved my livestock more than once! I moved in July and only moved about 15 minutes away but I still used the air pumps just to keep the stress level that much more down with my fish, I am moving again sometime next summer and hopefully it goes as smooth as the last move! Good Luck!
I've made 18-hour road trips with fish/corals/inverts (even a few large koi once) just by double-bagging them and putting them in decent coolers. I would not bother with the hand warmers or the air pump--especially for a trip that's only six hours. In my opinion, those tools only add the potential for something going wrong; the air pump could fail and siphon water out, using the pump would also require a non-waterproof container, and some of those heat packs can reach temperatures over 120 degrees Fahrenheit.
I can have them inside the car - not trunk -where the temp. would be regulated - the cooler is a great idea to help hold water temp. ideas.and I can have a couple gallons of water in there. Still think I'll want an air stone - the pump could be taped to top of cooler - no siphon worries. Thanks everyone for great
Done the 6 hour transport myself once. I agree with Jersey Bounce. I double bagged all the fish with plenty of air in the bag, packed them into a styrofoam cooler and kept a couple hand warmers ready in case it started getting cold. Never had to use the hand warmers (moved them in Dec) and everyone made it fine.
Sounds like these guys have more experience then me moving fish... so maybe just disregard my comment I have only moved them 15 minutes away and was thinking better safe than sorry. So good luck and sounds like these guys know their stuff!