Search ebay for black powder tubes. A bunch of people sell small tubes that have nice screw on tops. They are only about two inches long and work great. One guy sells two sizes and you can get as many of each size you want. I use the short ones to hold my powder charge and the long ones will hold three bullets in sabots. The link is who I have bought from.
You can use any tubes designed for pyrodex or triple seven. I don't like them though as they are so much bigger than you need. Only precaution I take with any plastic tube is I wipe them inside and out with a fabric softener sheet to eliminate any static electricity.
Power Tubes 
