Played around a bit in the shop today (after no real shop for 2 years!). Best guess it would take a Saturday to work out details and make the first such ammo crate. Sunday could be spent making 20 more, since the jigs etc would be done. If anyone actually makes one, they might want to make several. (I can see it now at the muster: someone sitting at the rifle line surrounded by crates of ammo.
I'm curious how the stocks of spare ammo were carried by troops on the march. Each guy was issued a quantity, but (especially after the LBH) was extra ammo carried in the wagons/pack saddles, and how was it packed?