I just built a semi-portable shooting bench for my deer lease using 6" purlins and 2" square tube. I say semi-portable because it has skids (runners) so we can pull it to different distances. It's actually light enough that two guys could load it in the back of a pickup if you wanted to transport it. It might be the best shooting bench I've ever used, dimensionally and stability wise and works for right and left handers.

I'm going to bolt some 50 cal ammo cans to it to hold shooting bags, stapler, targets etc. so they're always with the bench. I found an awesome roll-up shooting bag, that when unrolled, serves as a gunsmithing mat. When rolled up, it fits in a can. The Grouper sandbag

I don't have a photo hosting website and I'm on the road right now, but if someone wants to post them for me, send me a PM and I'll send the photo's to you.