[MP&C]

Looks almost identical to pickup bed wheel tubs. Got any U-pull-it yards nearby?

Short of that, radius dies in a brake or use round rod as your die in a Mag brake. Using a Bead roller you could use some tank roll dies. You could also weld a piece of thick wall pipe to some flat bar, clamp it in a vise, and hammer away. Gene Winfield uses various sized pipes welded together with a slight gap between to form rolls fairly easily, a budget slip roll, if you will..