The 3 bar rack comes apart quite easily, it uses a long threaded rod through steel tubes as spacers. You can used new threaded rod and aluminum tube (from Menard's etc welding dept.) cut to the new length. I mounted mine to aluminum plates with H-D Quick Disconnect hardware so they go on and off in seconds. If I was to do a permanent one, I have always thought about adding a 4th rail because 3 are just too spread out to look right.
I had this picture handy
I too love riding with the windshield off, just around town though.