Be warned. If you get involved with a specific unit they will likely have a certain box you will need to copy or purchase.
The Sketchbook series for F&I War and Revolutionary War also has cartridge box patterns - but they are generic.
Here is an EXCELLENT source of finished boxes (G.Gedney Godwin - the Sutler of Mt. Misery) to show you some ideas. I've been lusting over the Dragoon version with only 12 "holes" (that one uses tin cylinders) but much less bulky. Too rich for my blood, however.
http://www.gggodwin.com/CartGenie/prod-134.htm
At one time I had a "17 holer" like #435 from the above site I made and, even though it's a relatively small box, it is a pain to carry in the bush. Big, heavy and bulky.