My previous awning finally fell apart after 12 years, and the only area that fell apart was where the sun hit it while retracted. So I built my own cover for the new one, and I only use it while my 5er is stored in the driveway for more than a couple weeks.
I used white PVC drain gutter which fit over the rolled up awning just fine. However, it wasn't real tight and would slip off. So I cut some 4" dia. PVC Pipe into 3" long sections, cut them lengthwise and rounded off the sharp edges. I used these as "clips" to hold the gutter sections in place at the ends and the middle joint.