Looooong road trip with bettas, and I do mean long.

[Tikibirds]

I'm moving almost 5,000 miles in a few days. Since it can be as cold as -40F outside for part of this journey, what is the best way to move the fish?

They are going to be in the car with a dog and chinchilla as well.
I ordered 10 of those 40 hr uniheat packs and I read the sticky on shipping bettas but since I am not shipping them do I need to use bags? I was thinking coffee cups with lids so that I can change out the water every 2 days or so with pre-prepared conditioned water. However, I am not sure that is a good idea because I have no way to actually heat the new water up. Especially since about 2,000 miles of this journey is going to be through Alaska-Yukon-British Columbia (not to mention TWO customs crossings with 22 smuggled tropical fish).

I want to take cup holders and secure it to the bottom of the box and put the bettas in coffee cups. I do not want to use shipping bags because of the length of the journey and at some point I would need to open the bags so they can get fresh air. The first part of the journey is going to be very cold and lonely, not really anyplace I can stop to switch out water or anything.
how many heat packs would I need to use at a time to keep a box at a decent temp for the fish? Can I use a priority mail box or do I need to fins some styrafoam to line the box?