When I had my '72 K5 I never had the rear seat in it--99% of the time it was just me in it,or one passenger..
I liked going to tractor pulls and drag strips far from home,and camped out in it quite a bit..
I ended up making a raised plywood platform similar to Muddysub's for it..used 3/4" plywood,with some bed frame angle iron braces bolted in spots that needed extra beef to prevent flexing..
It could be removed quickly if it wasn't needed..
,I made it in 3 sections ,running across from side to side,hinged with piano type hinges I got off a P-30 step van's rear door at a boneyard..200 or so rivets had to be ground or chiseled off,but they were nice thick aluminum ones,and 5 bucks a pair!..
That allowed me to lift up the rear or front section of the bed to get at items stored underneath...the center section had a divider underneath (a piece of 2x12") to support my weight and keep things from sliding all the way forward you placed near the tail gate..
I made it so it went all the way from the back of the front seats to the tailgate,and just wide enough to clear the side panels..
I could put my Camping stove,sleeping bags,food,etc all under the platform and still have nothing cluttering up the "bed" above..
I used 4 metal milk crates at the corners of the platform ,to raise the "bed" up high enough to let a stock sized spare to slide under it,those also gave me a spot to store my bottle jack,jumper cables,some quarts of oil,gallon of anti-freeze,etc,things you wouldn't be needing that often,but easy to access if you did..
I put foam pipe insulation on the crates so the plywood wouldn't rattle on it and drive you nuts..
I also had a spare tire on a rack on the tailgate similar to the ones shown above...I like having more than one spare,it has saved my butt more than once...like the day a plank lying in the road I ran over with nails in it,and punctured both my right side tires..

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I put some of the closed cell foam mats sold for camping on the plywood with contact cement,then put indoor-outdoor carpet on top of that with some adhesive...it was very firm,but with a sleeping bag or air mattress,it was OK for sleeping...being 6'5" tall,I did find the lack of headroom a real pain though,litteraly--I had to remember NOT to sit up all the way,or my forehead would get gashed open by the sharp textured coating on the fiberglass roof...
I like my van much better for camping,at least you cant whack your skull if you sit up on the "bed" I made for it..still cant stand upright in it though,and a few days hunched over like that will put you in agony for days...
I made the "bed" for the van in such a way it folds up into a pair of "bench seats" running lengthwise from front to rear with an open area in the center for your legs...