I have to admit that my storage "system" is a mish-mash of containers.
I do keep it all dry. 99% of it is in my basement where temp ranges from 55 to 70 and humidity averages 35% in winter and 55% in summer. (I have digital gauges on the wall to record all that).
Most factory ammo is in original boxes that are packed into the plastic ammo boxes. Those plastic boxes are not metal ammo cans but they do have a gasket and are stacked so they don't get disturbed.
My reloaded ammo is the real mish-mash. I dont have boxes for a lot of of it. I have about 8 of those square, gallon ice cream containers packed full of loose 45ACP LSWC's. Each one holds a little over 500 rounds, but I only counted the first one and lost track at "500" Exact count doesn't matter, it's a bunch - for action pistol shooting. (Caution! Don't pick up the container by the little plastic strap!)
We get doggy treats in a clear plastic, screw top jar. I pack 22LR cardboard 50 packs into those - not sure how many fit but it's a bunch. I duct tape the cover to seal it even more.
I had a light-duty, plastic tool box that I repurposed to pack my 327 Fed Magnum rounds into. It holds quite a few, those are little rounds.
All of it is stored of plywood shelves that I built with 3/4" plywood on a 2x4 supports. 18" ctr to ctr maximum suooprt spacing. No visible deflection so far but I,m sure given enough time... I'll be too old to care. Or I'll have shot it all off.
One tip - regardless of your own methods of storage - take the time to label everything. It really sucks opening everything up until you find what you want when you could tell at a glance by reading a label.