Building a better rear bumper / questions

I would go to a local steel business where you'll buy the square tube stock and ask them. Yes, .250 is way too heavy for what you want to do. I built one bumper, on purpose, out of 3/8" thick square tube and it took a forklift to raise it to be bolted on. I did what I wanted it to and it's never been dented with all of the pushing I've done with it.

While I'm sure you can find it on the internet, the steel shop can tell you how much the various thicknesses will weigh per foot. They'll probably tell you that over the phone.

Bill