One may well consider a designated safe just for ammo. My ammo safe has walls the thickness of my Glock, solid steel, and is 3 feet square. It sits atop another safe I keep gold, jewelry and important papers in. The lower safe weighs 5,000 pounds and is moved via forklift. Forklift stacked the two safes together, that now sit 6'7" tall. Naturally, I siliconed the two safes together. lol
Price I payed for these two safes? Free. Look around, older (better) safes get left behind. Contact a business realtor, auction house, lock smith.
The top safe is full, of many ammo cans, wish the bottom safe was full. lol
IMHO, it is not prudent, to store a cache of ammo, or firearms, outside a safe. Pretty good video I discovered on new safes.
You don't want to put all your eggs in one basket. If you have a safe or steel locker that would work. I found a local LGS that had ammo cans for $7 ea. You don't want dirtbags to know all your hiding places! At $1/rd, it's like pots of gold in convent storage box. After you have been broken in to, you don't want to tell too much info.
For now I have them in ammo cans in my bedroom closet. But im going to get a job box and lock up my ammo inside of the cans in side of the job box. They weigh almost 200lbs empty and add a few thousand rounds and that thing will weight a hefty ammount.
I keep my handgun ammo in a small cabinet above the gun safe. I keep shotgun ammo in a military ammo box. in the "gun room" I keep my .357 in a concealed safe in the master bedroom suite, and a box of ammo with it. I have a single shot shotgun on the wall in the library, and a box of shells hidden behind some books.