Do whatever you want. Don't ask if you can't handle an answer that may disagree with your opinion. Your actions have no impact on us, we are only trying to help you stay safe and legal. I really don't care if you want to stand in a vat of gas and arc weld, but if you ask about it we'll send some information your way.
You are specifically asking about safety issues in your first post. We have raised other questions in the interest of safety, you take them as attacks and feel the need to argue. All of them are in your best interest, ignore them and make up your own answers if you'd like. Ours are certainly not what you are looking for.
Every drum on your dad's truck is DOT, that's DOT territory. To be stored in any of those warehouses they have to be DOT, even if they are sitting on the ground. Not because the DOT has jurisdiction in the warehouse but the other governing agencies use the DOT spec as a minimum in their own regulations, including the state of Oregon. Some even use the UN identification.
Maybe your dad, or someone at his company can give you the actual regs for storing fuel indoor.
My guess is the bare minimum of grounded and DOT approved container.