Air conditioner replacement

I think you could go with a smaller capacity RV roof a/c. 13.5k btu/hour is really overkill for that little space.

It's nice to have the extra capacity if you want to cool down the interior in a hurry but results in short cycling once it's cooled down, and it sounds like a jet exhaust. So it depends on how hot it is where you camp and how fast you want things to cool once you set up camp.

There are a couple options in the 9000 btu/hour range. Might or might not be a bit quieter, but ought to be a little less expensive and more efficient. Any of them should fit the standard roof opening.

I don't have and personal information to base a recommendation on. I see there are both Coleman and Recpro a/cs in that size range. The Recpro is advertised as being "quiet" for what that's worth.

We had a chance to have a demo of a Coleman Mach10 and that is what we went with when we ordered our new trailer. Much quieter than the Dometic plus it has a bluetooth thermostat so no fussing with wiring one of those up. It is not as streamlined as the Dometic but that wasn't a big deal for us.