This is a long thread. Earlier, I explained why that is not a good idea.
I want a sacrificial bumper to spare the frame in a moderate collision. The stock TJ bumpers are cheap and easily replaced. (Ridiculously easy; I've done it. Ridiculously cheap because of all the aftermarket adding-on yielding surplus stock bumpers on eBay.)
A bumper made of, say, 4 x 4 x 1/4 steel box beam would survive a moderate collision, but leave you with a bent frame.