NO I get it I know what an RTT tent is. I am just not fully grasping why an rtt has to be 10 inches thick with heavy duty canvas and weigh 100 plus pounds, IT seems to me that a good back packing tent which is very light < 5 lbs and can withstand a lot of wind could be used in the rtt saving weigh and height ( wind resistance) It would of course have to have a decent attachment frame to attach it to the vehicle and a pad of some sort, but I am just not getting why this isn't done. If I had money to throw around I would design them and build and market them just my thoughts
I had the exact same thoughts before buying my RTT. It is two very different products with different applications. It basically boils down to cost and durability. Yes, you can get an ultralight 2 person 3season backpacking tent that weighs in around 7lbs, but a fairer comparison to a RTT would be a 4 season canvas wall 3 person ground tent which is probably closer to 50 lbs.
I am estimating the majority of the weight on a RTT is the base itself, which a normal tent doesn't have. I would guess its probably 50 lbs or more. Don't forget it has to support the weight of up to 3 people with half of the weight cantilevered over the roof, so trying to shave weight here is either going to reduce strength to increase cost significantly by using expensive materials, and it's probably not going to feel very sturdy when you're 8 feet off the ground. The ladder itself on my tepui is probably another 10-15lbs and it also has to support a lot of weight. I have a cheap extension ladder in my attic that probably weighs half that and is about the same height, but I do not think it would hold up very well for tent use. So just setting up a platform you're already at 60lbs or more before you even add the tent.
The other item that adds a bit of weight is the travel cover. When I first got the tent I was surprised at how thick and heavy it was, again probably 10 lbs or so. A normal tent bag only has to hold the parts together and stays inside the car where its protected, but the travel cover is outside exposed to the elements and has to withstand the abrasion from random objects and flapping at 80mph. The rest of the weight of the tent is probably another 10 lbs for the mattress then the remainder is the material in tent itself. It's heavier because probably sees more stress than a normal ground tent due to the nature of the design.
So while you probably can build a lighter tent, and some companies have, it's always a compromise. The fact is there really isn't a compelling reason to save weight, it's on top of a car and not something you have to physically carry.. Even if you reduce the weight 20-30 lbs, it's probably not going to make much difference, and most people aren't going to want spend the extra money for that weight reduction
