I used to work at a propane supplier. The rules state; any propane cylinder containing more than 100 gallons of liquid propane must be 10ft away from source of ignition. I never understood why it did not include...... all cylinders. Just saying.
But storage wise; propane cylinders must be stored, transported, and used in a well ventilated space. The relief valve must always be in contact with the open air space.
Now with that said the plant i worked at had a shed in the way back, called the pump out shed. Inside sed pumpout shed their was ventilation fans that were supposed to be on 24/7 365. But they were broken. Also inside the shed was always 50 to 100 full or mostly full 100 gallon tanks (420lb cylinders). Now if untrust worthy electrical wiring isn't enough to make you think, the tank we pumped into was directly next to the shed. The hoses for the pumpouts occasionally would leak. Also the pump for the pump outs would leak from the head gasket (our mouth breather maintenance guy claimed to have fixed it 100 times). The electrics in the pump room had a lot to be desired. Now directly next to the pump shed and directly across from the pumpout shed was the bulk tanks. The bulk tanks held over 30,000 gallons of propane each and there was two of them. I hoped every morning that place would go up over night.
Anyways, the best way to store your protane tanks is to have a dedicated plastic shed outside away from dwellings. They don't readily explode without modification. But the relief valve can pop and cause a glorious fire ball that would make dinner near impossible to enjoy.