I just ordered a couple of these:
http://www.ebay.com/itm/231608343125
My wife and I sleep in the roof top tent, and the kids were previously on a 2.5" memory foam mattress topper on the sleeping platform inside the cap. The mattress topper is cumbersome and makes loading/unloading gear difficult (plus, it'll be nice to double up the rtt's mattress!). These trifold pads are lightweight and can be easily folded and stowed. Best of all - the pads can be used outside the truck - tents, hotels, sleep overs, etc.
The trifolds are the correct width at 27" for the "single", but they're a couple inches too long. I am hoping to just be able to squeeze the extra inches out of them. I'll try to follow up here after they arrive next Monday.