I use a similar method with some different twists.
If you don't want to use Milliputty, you can use air set modeling clay. It is usaully available at stores like Michaels.
For texture, I use a small sheet of fiberglass repair patch. After you have put the bag in place, I cover it with the fiberglass and with a wet finger, gently press the fiberglass all around the bag. When I remover the fiberglass, the bag has a cloth texture.
Hope this helps.
Rounds Complete!!