So I have casters (wttool.com, 600-lb load, swivel, two-axis locking caster, $20 each) and found a hunk of 1/8", 4x2 square-tube in my garage. I also have a hunk of 4", 1/8"-thick flat stock. I'm guessing that's enough to build the bases. I'm probably going to use 2", 1/8" thick angle iron for...