Mine is made from 1 1/2 Angle Iron. But ive seen some with 2 inch square tubing that look really strong. Do a google search and look for pictures of guys rigs.
If you are in Whitesboro go to KMC fabrication and talk to Marc or Mike. They are good guys and can get you a fair price. They may be 2 or 3 cents higher per foot than J&I but you will save that in gas money.
They are about a mile north of dons BBQ on the same side of the road.