We use a big bucket with a rubber flap in the bottom of the bucket in which I have made a lot of holes. when not in use as a flopper stopper, it hangs on the solar gantry and we store fruits and onions in it, it works great for that as eventual water do not stay in the bucket.
it works ok as a flopper stopper, but i think a triangular shaped plywood board with a small lead weight would be better as larger surface and rellatively easy to store.
Will probably manufacture one later.
Concerning rolling going down wind it's much less that one can expect, on our Atlantic crossing we run pooled out Genoa and Balooner for 6-7 days and the rolling was not a big issue, on the contrary very comfortable, and easy to furl when encounter squalls.
Paul on SY Kerpa SM#259