Count me amongst the RTT apostates. I had one and passed it on.
I had the first generation Car Top Tent. There were aspects of that make of tent that were undesirable (shoddy ladder construction, thin single walls, very drafty) that don't apply to other makes. Certain needs are fulfilled by the RTT, but for my needs, it wasn't suitable. The pros listed before are pretty dead on, but here were my reasons for getting rid of mine...
--Raised center of gravity. On top of an already lifted vehicle, off-camber situations are just that much more hairy. RTTs make a lot more sense on trailers, or low over the back of a pickup bed.
--They're too big and heavy. At 6' x 3.5' closed, and 100 lbs., they are a pain in the butt to store, move, put upon or take down from the vehicle.
--Set up and take down of the tent, as well as installation, was made more difficult by the fact that on a lifted truck, I had to climb all over to set it up. Taking it down was more difficult because the vinyl cover had to be stretched out and tucked in on all four sides. Set up and take down times were longer than with my ground tents.
--Effect on gas mileage. I was losing 2-3 mpg at highway speeds.
--Adding longboards on top of the RTT was a pain. It's just too high up.
--Without a changing room, there's no place to stand up and change.
--As mentioned before, toddlers are a no-go in the RTT. My wife wasn't crazy about climbing in and out of it in her platform flip-flops, either.
--Exposure. Less shade in the desert when you need it, more wind when you don't.
--No "night wheeling". Sometimes, I like to set up camp and then go explore the area. Once you've deployed the RTT, you're pretty much parked. You can't just leave the tent behind and take off. Again, this is rectified by a trailer.
Because I don't worry too much about being attacked by animals here in the southwestern US, the RTT on the vehicle makes less sense to me. I can see it in Africa or places where there is a real risk of animal attack. Here, RTTs only make sense to me on trailers, where they don't affect the handling of the vehicle, can be mounted lower, and can be left behind at camp. For now, I'll stick to sleeping under the stars in fair weather, or deploying one of two tents, the stand up, 10 person Eureka expedition tent, or my cozy little 2-man Marmot.
