Yeah I sleep in mine comfortably I'm also 6'2. The rear cushions need to come out, I usually leave them at home. Though I have also stashed them on the front floor boards when I've needed them on some trips. A air mattress is pretty much the only way to get the full length you need. After folding the front seats down there is a small gap between the folded rear seat backs and the front seat backs. A air mattress is well supported enough to simply balloon over it without you noticing it while sleeping on it. The rear seat folds almost level to the rear floor, again the mattress absorbs it to make it level.
I can lay straight flat with my feet upright and have maybe 3-4 inches before my feet contact the tail gate and about 3 feet of space above my head. It actually feels pretty comfortable plenty of room width wise and the full length of the mattress. The stadium roof makes roaming in or out pretty easy. It's outstanding camping in the Xterra. I actually sleep better in it then my current bed. Maybe it's just the alcohol around a campfire though, haha.
I use a twin bed air mattress as so I have some interior storage space on the side of it for stuff I want locked up over night or out of the rain. I usually pitch a cheap walmart kiddy tent to store my gear while I sleep.
Many others use a Full Sized mattress I've seen a husband and wife camp in the back of their Xterra. They said you had to be really close with the person you were sleeping with though, haha.
Getting in is easy via pop the hatch crawl in, getting out you have to twist to the rear door as there is no hatch release inside. I like sleeping with my feet at the hatch for whatever reason, I guess more head space.
Twin bed
Here is a queen mattress sandwiched in there. The beds are on a little tiny bit of a angle do to the seat backs but parking right makes all the difference.
If its hot a little bit of screen and a fan help though on about 70% of my trips it hasn't be necessary. Just those hot summer trips with no shade.
Storage shed
