My old roomate and I actually built a rack several years ago that sat in the back of my p/u bed between the tailgate and wheel well, In fact Brian u have used it if you remember. We made it out of wood where you can get 4 sets of gear all set up on the tailgate side and put 4 spare tanks on the opposite side. You would open the tailgate, slide the rack to the end of it then turn around and put your arms into the bc.
We would set our gear up at home, put it in the rack and then drive to the beach for our dives. We timed ourselves one time. Shaws Cove, Laguna Beach, from the time we put it in park we were changed into our wetsuits, strapped in, made the way down the stairs did our surf entry and were descending within 10 min.
Our BC's were weight integrated so that was helpful. We would use milk krates to hold our mask, fins, access etc.