First I'd figure out if the old A/C is running 100 percent like it should be. If not, I'd get that one up to speed. If that wasn't the case, I'd look for ways to insulate and/or shade the RV. If all that fails, I'd add a second A/C unit. It would take me a few drinks to get the nerve to cut the roof. I would want to know exactly where to cut and defiantly cut from the inside first. It something went wrong, I could fix the interior. I'd make sure the wiring was there before cutting the roof! I'd probably DIY the job but that would be one I'd hate to tackle! There's a bunch of stuff that could go south on you. Like at said at the beginning, make sure the old unit just doesn't need a little TLC first! You could always just drive north!
