I have used the method you mentioned of folding over the envelope for several years with no problems. I usually write instructions on the outside for the swapmeister to cut the tape to reuse the envelope. If it is taped up well for the return trip, it should be secure. All that being said, the mail is most often handeled with machines and things can get caught and torn open. I also have my name, address and email address on the inside of the fly container just in case.

Jim Smith