I was checking my filters on my AC a while ago and found the screws had come loose. So I tighten them and have had no problems. I have talked to other
Casita owners that have had the same problem so you might just open the bottom cover and check.
On my houseboat the gasket had gone bad this year and it leaked. Same kind of AC. It was easy to tilt the AC up on its side and place a new gasket under it and screw back in the screws. Gaskets don’t cost much.
It took us about 30 minutes to fix it and we hadn’t done it before. Sounds like your guy has a one hour minimum or something.
Good Luck.