Try www.horstguns.com/ShootingBench.htm I got this site from something on the Outdoor Channel when they had a piece about this bench design. I'm intending to use it on my farm and will probably cover it overhead for use in summer and rain.
At our club they built the bench in a shape of a C. You would sit in the middle so if you are left or right handed all you did was move to your left or right without getting up. The set was a board that you could move up or down for what ever reason. Just make it wide enough for fat butt people.