I took a couple of pieces of square tubing I had and welded a short piece of angle iron
to it, then clamped that down and that holds the tubing down better to weld it on the
ends.

I cut off 4 rings from a piece of heavier pipe because the fence rails are tapered and
I didn't want to have a bind on it, so I welded them to the pipe at the beginning of
the taper. I didn't have a problem with them sticking but these doors will be off and
on the car a lot so I thought it would be a good idea to put a stop there.

I put a straight edge on the cross pieces and the end pieces were a quarter inch lower 
and the next two pieces were 1/8" lower than the center pieces. It warped when I welded
the cross pieces so I cut off some pieces of steel and plug welded them to the tops of 
the cross pieces, ground the welds smooth and now the straight edge is on the money.

I turned it on its side so you could see it.

A picture of the stop-rings.

I bought this matting, it's about 5 feet long by two feet wide, it was $20.00, but it's
really nice and soft.