@Randun It really is a personal thing, I slept in a ground tent for a couple of years but trying to find clear space, and sometimes dryish to pitch the tent got tired fast. I then slept inside for about 8 years, but as my trips got longer that was always work juggling gear to sleep.
Last year I got an RTT, a small one Tepui Ayer 2 man, it is light (95lbs) and works well for me.
Setup and take down about 15 minutes a little more in the rain or snow
Fuel economy hit not measurable , but I drive an 04 LR Discovery II so it is not like I had any fuel economy anyway
Off road performance impact none, but I do not rock crawl and the Disco is heavy
Best thing here in the Pacific Northwest, if I can find a more or less level spot and a hockey stick of distance off the side of the Disco I am good to sleep.
A few things it will not really protect you from either bears or nosey racoons, they can both climb. I have not had an issue with either off roading, but I have seen raccoons climb step ladders
If it gets wet you will need somewhere to setup and air it out when you get home
They are not cheap
Most times you are not getting into any garages with one up there
You will need good load bars or a roof rack and those count against your dynamic roof load. (total safe weight up top when moving)
If you like to camp in one spot for day then explore each day you will setting up and taking down the tent every day. Not an issue for me as I go solo and tend to move a fair bit.