Charlie P.:

If you secure one sealing flap on the forward side only it tends to flutter all by itself. I have, however, seen loose flaps installed on both sides of the gap (or top and bottom) working nicely. But they tend to tear/separate from the forward surface where they are secured.

They do look good when they are new, and if you don't mind replacing them every now and then, go for it. Just don't do it on one side only.

Bill.