I don't understand the attraction of RTTs. A friend put one on top of his TJ and after a couple uses he took it off and sold it. After watching how long it took to get it ready for use, how long it took to put away, and having to put up with the ladder, I could see why he sold it. The tent I used took me all of maybe 2 minutes to get ready to crawl into.
Only if I was camping where there were dangerous snakes like Cobras, Black Mambas, etc. that are known to crawl into tents at night would I want a RTT.
They answered it, definitely useful up here. They are expensive and a big block of top weight on an already tippy vehicle I understand from your point of view, I really do, there are negatives, but if you camp A LOT, it is an excellent investment. Leave your pillows and sleeping bags in it... Leave it on year round if your jeep isn't your daily... And it takes no time at all to set one up, off the ground from all elements and a few extra seconds to scare a bear with a gun shot, instead of it just trampling you helplessly in your tent, guaranteed flat sleeping, if not add a rock under whatever tire needs it...
I look at it this way, instead of flying I could drive, have my vehicle to get around and being able to truly explore the hiking and national forest.I can drive my own vehicle, wing a trip an extra 500 miles any direction at a moments notice, explore, hike,camp, not be in a hotel, so one week vacation of hotel cost could pay for this tent in one year and the rest is just free hotel fee's for life, if you are an avid outdoorsman or travel, that's another way I look at it.
If retired, every day is vacation and you should be calling one of these your second home driving all across the u.s in a tj or lj, that's what I plan on doing