Not very hard in my opinion. I did mine similar to those above. Straight tubing cut slots on one side only and nearly in two and maybe 1/2" to 3/4" apart. Solid side down or up and it bends by hand. Care has to be taken to get the length of the piece right after taking it from straight to curved. You can leave it long and build to fit where the curved piece lays inside the sub frame pieces, tack it, then trim the length flush. The most time will be spent welding the cuts back up but the tubing/hump will be very strong and any shape you want.