Transformers, breakers, 500KV transformers in fact just about every piece of utility equipment use transformer oil.

So did the Heathkit dummy load. A 1 gallon paint can to be precise. It used an SO-239 connector gasketed to the top.

With the proper gasket and connectors this will work well. Actually I might suggest a vertical Pelikan case not too different looking from an ammo case. As for fires that is generally 20 year old oil in overloaded transformers. So when was the last time you fired up your Apple II ? Just do not use cooking oil!