am i understanding that the reason you covered it was to send it for less than priority mail? i've re-used those mailers by slapping a sticky label over the original address. i buy those 8-1/2 x 11 sheets of peelable sticky sheets and cut off what i need to cover the old address.
on the other hand, i've smushed fabric into plastic bags, layer on layer on layer. my favorite is black garbage bags. taped it all over, and sent stuff that way. i can't win no matter what i do. the only thing that goes at less money is media: books, videos, discs, etc. MUCH LESS MONEY!!! in the plain metal-clasp envelopes. i think the key is not to use those mailers. i think.