Just a heads up, I found these 1 pound weight bags from a company called Lineco. They have a very soft fabric cover and have a plastic inner bag (to keep the steel shot from rusting through I guess...)

They work GREAT for holding down sheeting, cap strips,etc... They're not cheap and you can probably make them if you have a sewing machine.
I'm lazy and just bought them.

This place has them and they get cheaper in qty. http://www.framedestination.com/prin...EI20000000000/

Lineco 1 Pound Weight Bag for holding down prints while matting or mounting them for picture framing. Provides pressure to hold glued items together while drying.Non-toxic steel shot weight with soft non-abrasive double layer cloth covering. The steel shot conforms to the shape of the surface. 6 inches in length, diameter 1-1/8 inches.

I love new tools.

PS; they come in 1/2 lb sizes as well, for smaller light weight models