we bought  the smallest Kelvinator one a couple of months ago for $350 and as we have a pop top 16 ft we put it in one of the fly screen vents  when we have power. A bit awkward but worth it. There was nowhere  that one could be fitted other than under the bed at the back and there it would not be very efficient. I had to make a padded frame for it to sit on to avoid any scratches and with some door stops at different lengths to have it sit on the angle required. We have to take it out before dropping the pop top.   Our solution, but it all depends on if you have a space where one can be fitted. We have just crossed the NT and now in north Queensland and when we have used caravan parks with power it has been fantastic. We have had many days in the high 30s and low 40s.   Good luck in your search    

We had a a Delonghi portable too in or old 16 foot caravan and ducted the exhaust through the floor. Worked really well and even worked off our ge#@#@tor at the time.

We purchased a small AC from bunnings Darwin last May. (We we there too early and it was hot!) It was shop soiled but worked well. I mounted it under the sink eventually with a hole through the wall for the tube and an external floppy vent on the outside also from bunnings (l dont have shares) The beauty is, one can take it out when at home and use it in a bedroom, a room the house aircon doesnt cool well. Cost us $200