My truck bed is only 73" long. A two leg version of the Roll-A-Cot fits pretty well in the bed of my Tacoma when the tailgate is down and rear canopy hatch in the open position. As mentioned, the floor could get wet or dirty and you'll still have clean sleeping area. Plus, the cot stores out of the way, when not in use.
While the Roll-A-Cot clears the wheel well, it's 15 inches above the floor, which leaves no room to sit up under my mid-rise Leer 180 canopy. Also, in cold weather, you'll want some insulation between you and the cot, which raises its height further. So, the cot only gets used in my 4 person tent, which has 5 feet of head room.
When I sleep under the truck canopy, I use a 1" thick pad of closed-cell polyethylene foam, (
http://www.foambymail.com/PE17-_2/polyethylene-foam-sheets-1-7lb-blue.html ), in cold weather I add a reflectix radiant barrier on top of the PE foam sheet that is only about a 1/16th of inch thick, and on top of that my Exped Downmat XP9 inflatable pad. The advantage is I can sit upright, while I get dressed.
For the extra leg room, I have to lower the tailgate and raise the rear canopy hatch. To keep out mosquitoes, I have a screened cover - which you'll find is 20% off with free shipping at Campmor right now.