There are several places you could place a small Optima, since they don't outgas and can be laid down on their sides, you can place them inside the cabin. In the left rear lower panel where the rear heater and a/c are in some models. Under the second row seats if you never have to lay them out flat for cargo. Outside in brackets that hold it in place behind the rear wheels next to the tow hitch on rear frame. and Just behind the front bumper opening in front of the radiator. In place of the winshield washer bottle (move it somewhere else like the other side of the engine bay.