so what I was thinking was that I don't really need the bumper wheels.
My concern with the headwind unit was how to put wheels under it.
I don't want to drill holes in the roller frame or the head wind unit frame - the legs are box structures and I don't think I could drill accurately.

I was thinking about getting skateboard trucks mounted on 2x4s that go under the frame, and building the door frame bungie assembly with bungies attached to the trucks. I could also put trucks on plywood and stick the headwind unit fan on that item. Just a concept in my head right now.