I have a coleman 15k BTU and working on some modifications.
If you take the cover out it flows 4x more air so I'm working on this modification. The difference is insane. You can also test this by simply removing your cover(almost all of them work this way) and turning the unit on. Prepare to be blown away.
Coleman/Mach AC Mods - iRV2 Forums
If you have one of these units you need this in your life.. Trust me.
The stock thermostat in most of these units shuts down @ 78 degrees so you can modify the analog or wire in a wall mounted thermostat that will actually shut down the fan when it's not cooling.
You can also wire in some ducting and a 12v bilge blower for the rooftop parts.. Really helps not only the unit but to pull away the hot air so you can use it while on the flybridge.
Mine has lasted about 6 years without any sign of quitting FWIW.
Once you do both of those things I really say it's the best bang for your buck. They are loud but once you get them running right and a thermostat wired up they don't have to run 24/7.