I will answer this with the expectation that the conditions mentioned by cj001f are soon forthcoming . . .
If you fold up the back seats in the 4run the back space is exactly 5'9". I am 6'1"
Rip out the seats altogether and it could work. Or, if you actually have a functionaing tailgate, just lower it down and you can have your footsies in the rain. Would be cool to create some kind of two-tier storage/sleep thing back there. Ahh, miss my 4runner but can you miss something when it was you who in fact killed it