You kinda have to decide between a proper airconditioning unit and an air cooler. The first has a compressor and is a heavy piece of kit. It also requires a hefty amperage. Very nice in the hot weather, but to carry one in a caravan I would suggest is not practical.
Many people have used air coolers which often use cold water to provide the cooling. They are much lighter and take less power. Obviously they are not as efficient but can be a good compromise. Or you can be like many of us, open all the windows, get a good fan, and sweat. Actually, usually by early morning it has cooled sufficiently to be fine.
Unless you have a pantechnicon as a towing vehicle i would suggest that airconditioners, even the very smallest may be a load too much. If you have a motorhome however, then the option is very much more a practical issue.