Gasoline and propane should never be stored in an enclosed space, especially an attached garage. We have a strategic petroleum reserve of about 60 gallons, all in 5 gallon NATO cans. Those cans are airtight. They are stored in an unheated outbuilding with an open door. 20# propane tanks are stored outdoors. The 55 gallon drums of ether are stored in the kitchen, next to the woodstove.