I don't have pictures....and I'd go take some, but I have class, and someone rearended me the other day and my tailgate doesn't come down anymore....so I couldn't really put tanks in to show you how they fit.
I basically bolted a 2x4 along each side of my bed. Put some eyebolts in. Strap tanks in.
Works well. I actually made an L shape with 2 2x4s and cut out spots for the tanks to go in, but the straps hold the tanks reallyw ell, you don't need the bottom of the L at all. A buddy just has a 2x6 on each side with eyebolts and his rack works great.
Observations: if you have an open bed, lock your tanks down. If you have singles, get your dive shop to put SS rings around the valve, you'll have to drain the tanks but it'll let you lock them. Run steel wire through the rings and through an extra eye bolt and lock them down! Then you can run inside to grab a bite to eat after a dive without worrying so much.
Also, if you get rear ended like I did, tanks in the back corners are liable to get hit. Might be wise to strap them in the front near the cab. Fortunately, I didn't have any tanks in the truck. If I did, I think they would have survived, but I wouldn't want to test it. Now I am goin gto start being MUCH more careful about how I load things, never been in an accident before and it made me think about how much stuff would or could go flying.