I never pulled the trigger on a roof top tent, but when I was weighing out the decision to buy one a while back, the two biggest pros for me was that a roof top tent will keep you off the ground. The ground can suck the heat right out of you. This and ease of use compared to finding a good flat piece of Earth, kicking all the rocks out and all that set up. What ultimately kept me from pulling the trigger on a RTT are 2 cons mainly. The first being that I cant really set up camp until I'm done using my vehicle for the day. If I suddenly had the urge to drive out into a clearing to do some night photography or something like that, I would need to break the tent down. I also now have a young son who comes camping with us, and I just don't trust him yet coming in and out of a RTT via ladder. The other con to me was the reduction in MPG I stood to lose. My vehicle is a brick as it is, and my truck is also my daily driver so I would be compelled to pull that tent off my vehicle and put it back on whenever I went on a trip.
This isn't to say that not getting a RTT is the answer, it was just the answer for me. I know plenty of people who run them and love them, but for my situation it wasn't the right choice. I have found a fix for using ground tents and staying off the ground and it isn't an air matress. It is a little more pricey, but if you or anyone else wants to stick with ground tents but sleep like a baby even in the freezing cold, look into the EXPED sleeping pad. It costs a few hundred bucks, about 400 for a full size version, but it is hands down the best sleeping pad I have ever used. They don't take up much room when broken down and packed up, and feel just like your matress at home. I've been sleeping on the ground and under the stars for decades, have always been anti-air matress, but this is so much better than an air matress or anything else I have tried through the years. So a decent tent, an exped and a quality bag, and you are housed for the fraction of a RTT, and you don't need to pull the tent off your vehicle when you are back in civilization if your truck is also your daily driver. Just the solution I have recently come up with that works really well for me and my family.
