If your ammo can still has a good rubber lid seal no desicant is needed or necessary.
Mosture cannot get in unless it was already in there when you closed the lid.
GI ammo is not packed with desicant when it is manufactured, and it travels all over the world in every kind of weather.
I use Zip-Locks and ammo cans, and have reloaded ammo stored that way still like the day I put it there 30 years ago.
rc