back bag question

ok im sort of new to minitruckin. i was just wondering y there is a bar form one side to the other on the back bag setup? do u have to have it? im not building one right now but just trying to get ideas. couldnt u just weld it to the frame and the axle and it work.

That bar is there mostly for support, remember...you just cut your frame so the more supported it is the stronger it will be