I've now got over a hundred nights (not in a row) using the leveling platform noted in one of my above posts, between my old '14 TE and my current '17 SR5 and my wife's current '17 SR5. Continues to work great for two-person or solo trips.
It's worth noting again, because I think 3rd row people don't always understand, if you
don't have a 3rd row and don't have a cargo tray, the rear seats don't fold flush with the cargo area floor, so you need to have a filler of some sort to raise the cargo area floor about 2.5".
I think for $30 in wood and an hour of labor, this is the best upgrade you can do to sleep in the back. Perfectly flat, copious room. On my last solo 11 day trip in March '18 I was able to renegade camp quickly and easily every night because I was totally self contained. Several nights I let the truck run all night to keep warm as it was in the high 20s - benefits you don't get with ground tents or RTT.
Here's a few more pics of the pallet (and 8 gal Rubbermaid Action Packers in the foot wells) that drop in there to make it flat:
With gear:
Gear stowed and 'full' mattress and bags out for two person use:
Gear and double stacked Thermarests for one person use: