I'm on my second. The first was a SunLite Eagle on a Chevy 1500 4x4 with an air conditioner on the roof. Second is a NorthStar 850 on a GMC 2500HD 4x4 with no air. The first was actually only about 6 inches taller than the second. More of the height difference has to do with the truck tires and suspension since the second truck rides a lot higher than the first. While I've never measured them for door clearance, I know enough not to take them thru covered bridges and low clearances.
As far as air; the only time I used it in the first camper was in the driveway. It did cool the camper down quite well. I don't really need it and as previously stated, there's plenty of windows to let the breeze blow thru.