I used 2" square tubing, the same configuration as the front of urs, bolted first , then welded. The back of mine are actually slid inside the rear frame and welded up , it put the 2" tubing in the floor about 3/4", so they had to be welded all the way/ took 3/4" foil faced foam board ins. to fill and even out the the void before new carpeting, can`t tell anything is even there. keep it coming, we like ur work and posts !