I am not a reenactor. I've been to an event or two as a spectator, and don't recall seeing anybody with a powder gourd.
However, I've gotten the impression that a lot of reenactors may "latch on" to some trait or feature that was not very common (e.g. brass rings on hunting pouches) while ignoring some old-time practices that were actually pretty frequently encountered, such as powder gourds. It is my understanding that these were not uncommon, at least in the south.
We have two powder gourds in the family. I'm sorry I can't post pictures... they are at my brother's place. I'll try to get photos and post them, but I can't say when. Anyway, one of them is about the size and shape of a hundred-watt bulb, but with a smaller neck. It appears to be plugged with a cork, but it may be tupelo root. I recall my dad had a big chunk of tupelo root when I was a kid. It did indeed have a cork-like texture and weight, and I remember he told my it was used for many things back in the day, such as floats for bream fishing. This gourd is plain and unadorned, but it has a nice polish from handling and use. It was originally owned by my great-grandfather. Dad said G-grandpa's wife (Dad's grandmother) would borrow the powder gourd to use as a darning ball for mending socks! (Another lost art!)
The second gourd is one my dad grew when he was eight years old. He nailed together a small box of rough lumber, and placed the immature gourd in it while the gourd was growing, so it grew as a square-sided gourd which would stand up on a flat surface. If memory serves, this one was about six or seven inches tall and maybe 2-1/2" square in cross section. I think it has a stopper similar to the other one.
Dad was born in 1907, so this second powder gourd would date to about 1915. He grew up shooting muzzleloaders, and these guns were in common, if not general, use in the more remote areas of the deep south until well after WWI.
Like horn, gourds do not "sweat" with eposure to a rapid change in temperature. This is one of the chief complaints about metal powder flasks, in that the powder may become contaminated by condensed moisture if you bring a cold flask into a warm room. Gourds are not completely crush-proof (see George's post #8, above), but they are surprisingly tough, and they are waterproof. They don't really need any kind of coating or treatment. They were used for storage of many commodities, and in fact, there is a favorite old-time fiddle tune entitled "Sugar in the Gourd." For that matter, large gourds were even used to make banjos. Here is a modern rendition of a gourd banjo from Jason Romero:
Best regards,
Notchy Bob