Nixy's got the right idea with packing something in between the pots so they don't move or tip over. Also, tommy's is a good idea too on covering them with plastic. Anything that's going to insulate them from the cold. I wouldn't leave them in a truck too long, and make sure they're the first thing off. Do you have too many to fit in a car, so you can control the heat and don't have to cover them up?
When I moved, I took cardboard boxes and pressed the top flaps into the box so they were flat against the sides. Then I got a ton of styrofoam peanuts and lined the bottom about 3 inches thick. Then, one by one, I put all the pots that were similar sizes together and squished in the peanuts between them. That way the pots wouldn't move around or tip over.
Here's the thing though, I wouldn't put my plants in closed boxes. I insisted they go in the back seat of my (climate controlled) car so that there was no chance of damage. They can be very sensitive to cold, and they could suffer a lot of damage if left in a cold truck for a long trip.
As far as watering goes, I wouldn't deviate from your normal watering schedule unless you're planning on leaving them in the boxes for quite some time. In which case they'll go into shock anyway with the temperature changes, lack of light, and lack of air flow.
