During the day my concern would be are you stopping to eat and staying in the car while you eat, thus keeping the temperature pretty consistant. Even with mild temperatures it gets warmer in the car even with the windows cracked, so if you go inside to eat be sure to check for large temperature changes (before you go in, half way through meal and when you get back to the car). If the temperature climbs pretty much I'd have some cups (like you buy them in) and put them in paper bags to take in while eating.
I'd keep the heaters to where they could be used at night if they seem to get sluggish at 68.
One thing I would do for all the animals is take some jugs of the water they are use to drinking plus the fish are use to having. Fish need to acclimate slowly to water changes (hardness, pH, etc.) and if your going 2000 miles you will end up with probably variances of these in the water. On the road if you use any new water for the fish, what they are use to is best. When you set up the tank again slowly acclimate them to the new water.
As for the dogs and cats having some of the water they are use too will help them keep them from getting upset stomachs or having loose stools. Some animals are very sensitive to food/water changes while others aren't.
If you can find some Methylene Blue (Zinc Free-tints water blue) it will reduce any stress they may get and helps lessen the effect of ammonia and nitrite poisoning. It will stain you or anything it comes in contact with so it's generally used in bare tanks, plus it kills the good bacteria so it's not good to use in cycled tanks. It aids in preventing bacterial growth and will kill most parasites. Most pet stores use it in the little containers they keep them in. Got mine at the local small pet shop, not sure if PetMart, etc. carry it but Wal-Mart doesn't. Handle it with rubber gloves on and keep the bottle in a zip lock bag in a container it can't get smashed in. One drop per gallon or even 2 gallons is probably enough and no need to add more unless your changing a lot of their water. Later it will come in handy if they get sick, but only use it in a quarantine bare tank. It won't stain glass and think it didn't my acrylic hospital tank, but it will gravel, etc. If you have any plants I wouldn't keep them in it either.
Have a safe, fun move!