I've got two one is commercial 3 legged design I believe I got it from Cabela's, which weighs in at 50#, and is extremely stable. The other one is handmade from the directions from an old NRA article, using 3/4" plywood, covered with felt with a piece of 2X4 screwed and glued underneath the piece of plywood. Note: I cut the plywood in an L-shape for right hand shooters only, but it could have been cut either way. The top then goes on top of an older Workmate work bench, and I use a padded small stool for a seat. Works for me and mine and again is very stable, the only drawback is you have to carry a lot of gear just get it set up, but once done it definitely does the trick.
Not nearly as neat as a steel bench, but not nearly as permanent either. Kind of reminds me of when I first moved out here, when I went to the local public shooting range which is not monitored and erected a shooting bench which I thought would be permanent, 4X4 legs, 2X2 top and a seat made of wood and attached to the bench. Indoor/outdoor carpeting on the shooting surface. Covered all the wood in Thompson's Waterproofing solution, and sunk it in the ground approximately 2'.
Needless to say a game warden friend of mine commented on what a neat bench, but I doubt it will last very long. He tried it and thought this is definitely the cat's meow.
Well he was right after having used it 4-5 times myself I went out there and found the bench all shot up, and eventually burned, therefore I use only portable shooting benches, except when I go to my monitored gun club.