I'm late to the party, but you can do it. I'm 6'3 and have spent at least 60 days sleeping in the back of my 4Runner over the past few years out in the wilderness.

I came from a Grand Cherokee, and one of the first things I did there was to install quick release pins to be able to take the bottom of the back seats out. Since that technique doesn't work on my 2004 4Runner, I just grab my ratchet and socket, and unbolt the things. Takes another minute or so, but it's not bad.

Once the seat bottoms are out, I lay the seat backs down, and use a 4" memory foam twin mattress for my sleeping pad. I put my head at the tailgate, with feet up near the back of the front seats. Blankets for cover, and my dog and I do just fine back there.