I've had to move my indoor plants cross country during the winter. That is almost easier to do than in the summer. There is also the problem with hot days and cold cold nights. This adventure sounds about a five day trip?
This is what I learned to use for transporting plants in the winter as well as the heat of summer. Newspaper is your best friend. I assume a closed trailer, yes? The best of course would be an atmosphere regulated trailer but I've not seen those available thorough Uhaul,yet.
Heat over 90 will start cooking your plants. Temperature drops more than 5 degrees below what your Bonsai are used to and that could set them back or kill them. I am guessing your bonsai are both indoor and out door in Colorado. Or just indoor?
You will want a good 'fan' that can run off the battery or be plugged in at night at a rest stop or KOA. There are lots of areas you will be driving through that will have 100 degree F plus daytime and 20 below freezing (32 degrees) or 12 degrees F. It may have been common knowledge to everyone else but 12 degrees F doesn't mean as much as saying 20 below freezing.
This is what I would do. Bonsai aren't 'replaceable' and they are also very very fragile and have exacting needs. Soak your plants of course. Put them in a big plastic bucket when filled with water and dump the entire pot until it stops bubbling. Shake gently and allow to dry.
Spray your plants including the top of the soil, the branches, the undersides and topsides of the leaves. This leaf shine stuff actually puts a layer of protection against extreme temperature changes, stress of moving, etc. Spray both sides of the leaf. Neem mixed appropriately in the right amount makes a leaf shine. But don't use Neem if you can help it. Only use if you are unable to find 'Leaf Shine' made just for a little raincoat on the leaves. This is not about insects at all.
Leaf shine stuff slows transpiration, reduces stress.
Using dampened newspapers, crumpled, loosely making a 'bed' for your plants to ride upon. Think of newspaper NESTS. Tie up the loose ends loosely above the plant like an Easter basket. Leave lots and lots of air above the plant and below the newspaper. Think of air bubble packaging. Crumple the newspaper around and below the plants. Tie so that you can release those ties most of the trip, tie the tops when in freezing weather. Cover the group with light covers of newspaper or even Reemay, cut to the perfect size for your grouping. Only for freezing temperatures, cover as another light layer of insulation.
Otherwise, open up the newspaper or burlap coverings and have that fan blowing 24/7. Spray to water heavily every single day. Moisten the newspaper and/or burlap lightly when high temperatures. Try to dry out before the night time cold temperatures hit. Just the stress of huge temperature changes, huge to your bonsai, could damage or kill your plants. 5 days is a long time. I'd be thinking about a simple grow light back there as well. To mimic the times of the day your Bonsai had sunlight or whatever light it was used to in Colorado about 5:30 to 9:00.
Sorry this is a huge answer. The more I considered this problem the more I could see that it wasn't that simple. 3 days, 2 nights would be max for no light. Open the trailer doors often during the heat of the days. Close them up at night. Keep the fan going.
Bonsai are different than other plants! All the work and time makes those guys precious and fragile and needy. Now I am ready to drive to AZ from WA state!
You could also use cheapo burlap, comes in rolls in the landscape division of Lowes, Home Depot, etc.
Not only will this mitigate the temperatures it will also protect your plants from being knocked around, it will absorb excess moisture and the wicking of the water out of the newspaper cools the plant, somewhat. You have to have fans blowing 24/7. At least one. That air should blow your hair around when you are in the trailer with your plants.
Get a cheapo sprayer from Lowes or Home Depot. A one gallon hand PUMP sprayer ($11.00) or a 5 gallon plastic pump up the pressure. They both come with wands to direct the spray either for watering or remoistening the newspaper lightly when it is hot. Allowing it to dry before the temperature drops significantly at night.
Are your plants indoor or out of door plants, normally?