I like Chris's idea.
I have a similar issue. 32 ft 5th wheel with 3 slides and a 15k AC and 30 A system. It's not enough on real hot days.
I already have one of those portable window AC units / heat pumps. So I recently set in up at the back of the trailer and set up a piece of wood to fit in the window track for the vent. I will take one of the swivel rockers out to give a little more room and weight trade off.
If you decide to try one, get the kind with 2 vent hoses so it doesn't suck your conditioned air back out of the trailer.
Haven't tried it out yet in the real world. But, it will get a good test in So Cal this august.