Jim, I used the same gates as yours and cut the bottom off to make them self cleaning (before I upgraded my DC). I put a flap of aluminum tape over the end to form a kind of loose seal that would pull against the gate when the vacuum was on, but I don’t think it was necessary. If that small of a leak sinks your dust collection system, you’ve probably got bigger problems. 

Ryan/// ~sigh~ I blew up another bowl. Moke told me "I made the inside bigger than the outside".