That's fine for a single vehicle and I do that, but for the poster that may not be a practical solution.
I also have a need for gas storage so my solution was to build a concrete block structure for gas can storage, vented and covered in dirt 18" deep.
Welded up a door frame and 1/4 steel plate for a door.
All stuff I had around the place.
That gives me gas for generators, the 4wheeler, the wife's car, and the tractor,etc..
Additionally, no vehicle or piece of equipment is ever allowed to get more than 1/4 tank lower than full...we probably have 300 gallons of gas on the place as I write this and 350 gallons of diesel.
I'll be putting in an underground storage for gas later this year, but the problem is still stabilization...I use Sta-bil(tm) and rotate gas out every 6-9months...never had a problem.
To the OP, if you're looking to store gas for a getaway to a safer place, the gas cans are enough, just rotate the fuel...if you're going to stay in place and defend, it's a different story...
You better have a good understand of the permitting required and double-wall tanks with leak detection if you want to bury gasoline.
And you should expect it to go bad over time.
The gas will be always available, the only question is what will they ask for it. The OP can set aside some money (comes in boxes marked ".223") for an emergency purchase, if the getaway is the main goal. You don't want to store too much gas anyway because you can't take all of it with you. You'd have to buy on the road.
if you're going to stay in place and defend, it's a different story
Only if you want to illustrate an indefensible situation :-) In the Mad Max world gangs will have numbers and weapons, and they will be after your fuel. To defend yourself you need to match their numbers and weaponry. You need a small village and a defensible terrain, and even then you are just one RPG hit away from a fiery disaster. Who said that a gang can't use a helicopter or a mortar?