Portable air conditioner

The other option is a small mini split heat pump. But with a fifth wheel, I imagine your current unit is in the living area, and the best place to mount a mini split comp unit is on the rear.
mini splits
The only one I know of under 9000 btu is a Mitsubishi 6000, Mitsu
But its pricey.

The fact that the entire unit is in the same room with you makes them noisy and bulky.

The need to run hoses to the outdoors makes them inefficient, due to heat losses through the hose.

Typically, a window unit will do a better job of cooling, even if it has a lower BTU output rating. It'll also cost less.

How long is your RV? Is there a roof vent that could be replaced with a 2nd rooftop A/C

The ones with two hoses (air in and out) on the condenser side are the only ones that are any good. Adding A/C capacity will help; but don't overdo it as you need run time to keep the humidity in check.