Thats an AWESOME design.... I only wish or suggestion is, to make the sides shorter, to make the finished product just a little more headroom. Im a short guy and did a sleeping platform in my other 4runner, it was right at the same height when done with the mattress and I would bump my head waking up, it was hard to actually sit up in the bed...
When you come up with a 4th gen 4runner design, I may have to jump on it.
Major Props to you