I use evaporative coolers in my Las Vegas house and top-end $1500 unit does work well, but even in dry Las Vegas we do have higher humidity seasons when it will loose the efficiency.
Considering risk of water splashes and limited use, I vote against putting it on RV.
For my latest conversion I order low-profile AC
From Rec ProIt really is low-profile unit, although not small and is having good referrals. I did not use it yet, but for me typical AC with their high profile are looking like balloons on TC.
Notice that I order 13.5k for smaller Sprinter van.
We had 12.5k on our Lance camper and in 120F heat it was barely making it. Opening any cabinet was like opening an oven.