OldSub is right. Another consideration: I sometimes step on the bumper when checking under the hood or loading stuff in the box. Try standing on a pipe bumper when it's wet; tough on the shins - owww!
You can get square or rectangular steel tubing in a variety of sizes. This stuff is properly known as Hollow Structural Section. I am thinking 2x4 or 2x6 would be good for a truck.
Here's an example of what you can get:
HSS sizes This stuff is commonly used in construction. Check your yellow pages for a steel supplier near you. Ask them what sizes they stock as not all suppliers carry all sizes. If you are not doing your own welding, the steel supplier would probably know the name of some good welders.
