Your about to get tons of advice. I keep mine in a very air conditioned environment. If I did not have that available. I would vacuum seal it with silica packets inside, then put it in ammo boxes with again silica packets in them. High and dry is the old but simple explanation. Some of mine is as I descibed and air conditioned.
A) load with military primers. Also for SHTF make sure you seal the bullets and primer. Lacker system is good and
when your reload you do it with brand new powder and components in a dried, clean and controlled environment.
Any contamination has the potential to ruin your long term loads.
B) Find air tight containers. Anything will do. There is no need to vacuum seal the containers but to make sure they
are air tight so no moisture can get inside. Even plastic jars will do if they are completely sealed.
I found some ammo boxes to be excellent and some others plain junk. The material and seal was not so good.
C) Then it is important to store the amunition is a dry and safe area and container and make sure they stay away from
any extreme temperatures. So in a shed ouside is not good. Also some food containers, sealed tool boxes, PVC
are good ways. It depends on your area space and how it is better organized.
Like fullmags said high and dry is better than in a humid basement somewhere in regular ammo boxes although
if one has a dry finished basement with climate control that would be as good as anything else.
Also no attics that are at 120F. in the summer heat and -20 in the frigid winter.
Keep your ammo dry and oil free and it will outlast you. I have fired 100 year old ammo. No need to repack. No need to do anything except keep it dry. If you are in a humid environment throw it in an ammo can with a dessicant pack and you are good to go until the can rusts through or the gasket goes bad.
As a test I stored a GI can full of ammo with dessicant inside in the can - exposed to the NY weather for 5 years and although it was rusted outside, the contents were perfectly preserved and still went bang. Obviously make sure your ammo is in a secure place so children will not get to it etc.