I'd use coolers, or if you happen to have a 10 gallon or less you can use that too, it's a pain in the !#$ but if you fill it about 1/4 of the way full with water that is already good, like from the tank after a recent
water change, and put your fish in there with some decor just so that have something you should be fine. I'd also suggest not using the bags, the coolers would work wonderfully (btw are you talking about the polystyrene foam coolers that chip appart at the slightest pressure) if you are just be wary that they do fall apart easily though leeching of the styrene into the water is almost non-existant. Do however keep them in the car with if you use coolers or if you use the tank method, since there won't be anyway to cool it while you are on the road. I wish you both the best of luck and let us know how it turns out,
Inari