I have a 2012 LE, and am going to pickup an air mattress to toss in the back for camping. Does anyone know what size, or a particular brand/model would fit best in the back with the seats folded down??

I bought a cheap one at Walmart (Intex brand?) in the twin size a few months ago and used it for the 2nd or 3rd time last night.
I don't remember the exact dimensions, but its approx 74" x 39". Width is not an issue; you'll have several inches to spare. Length is tight. I air it up from the back hatch with the front of the air mattress resting on top of the folded back seat. With the back hatch closed, I open the back door and jam the mattress down so that it lies flat. If you're about 5'9" or shorter, it'll be perfect.

I'm a hair under 6' and I can't stretch out fully in the 4runner unless I lay diagonally which doesn't work with the air mattress. I'm going to try one of the more compact backpacking mattresses and see if it'll fit diagonally.

I've been looking at truck-bedz.com air mattresses.

You might ask @J-BlickPhoto what he uses (as seen in his post under "What did you do to/in your 5th Gen Today?")

What did you do to/in your 5th Gen today?!

I use this: Amazon.com: Coleman Packable SUV Quickbed: Sports & Outdoors

It fits if you don't inflate the "pillow/head" section.

i have a coleman twin mattress.. fits perfect.. it sticks out a little.. but when you shut the tailgate door it snugs right in place.. i used blankets and stuff to fill in the sides when my gf and i slept in there on it..

Thanks guys. I was checking out the Coleman, and based on the dimensions we have to work with that appears to be a great option.

I just came across these air pads made by ALPS, which also seem like a good alternative. Anyone ever used one?

Amazon.com: ALPS Mountaineering Comfort Series Air Pad: Sports & Outdoors

This is the one 4Runner accessory I haven't seen yet on this site

Take the seat bottoms out, use the internal pump to blow the mattress up (all 4Runners have the amp in the back, right?)