There's several workable ideas in the Storage section. Depends on whether you insist on leaving the 3rd row mounted in the vehicle.
There are a couple well thought out builds in the big stuck topic at the top there which show platforms that extend or unfold into different configurations. Several of those ideas can be adapted / made to work
Additionally, most of the Suburban interiors can be made workable as-is. The 3rd row back folds down flat over the seat and is very close in height to the stowed 2nd row seat bottoms. A platform could be made which bridges across these elements and has supports over the voids. Such a platform could be hinged down the middle fore to aft, so the platform flips onto itself such that one of the 2nd row seats could be used and folded down and arranged for sleeping.
I'm working on storage drawer / platform idea that has some flexibility in it. The end goal being to have an extension piece that attaches to the front of the drawers / platform and extends over the 2nd row seats in their folded / stowed configuration, providing a sleeping platform space that 7-1/2' long. -
http://forum.expeditionportal.com/threads/161631-Storage-Drawers-Platform-for-my-GMT800-Suburban-WIP
I'm refining the platform extension idea now, hoping to hustle on it as I want to make a photographic trek up the 395 before the record snowpack in the Sierras melts off.