I love the flat rate shipping deal.. it is the best deal the post office has going. In the good old days when you could reinforce the package with tape to withstand rough handling by the post office I mailed a complete mint sewn bag of 1968-s memorial cents (5,000 $50 face) in one package setting a personal record of 31 pounds, 14.6 ounces. I used to mail at least 2 18 pound packages every week. The post office marketing department came up with this new rule about not allowing tape on the outside of the package. This has made it a bit tougher, but 8 pound packages are still very easy. The trick is to make an interior sleeve by trimming the edge off another priority mail envelope and folding the sealing flap all the way down. You then seal this interior package with all the tape you want and slide it into a fresh Flat Rate priority envelope. Fold over flap and seal normally.. no extra tape required. There is a 4 pound weight limit on Global Priority Flat rate shipping and the PO may put a weight limit on the domestic flat rate envelope in the future. Hope this helps Robert.