I have a Searay 220 Da with a 5.7 Mercruiser. The fuel cap is 60 gals. I need to extend my range. When I go to Lake Powell I usually end up bringing addtl 5-6 5gal plastic fuel containers which take up precious room. I have all kinds of room in the engine compartment for another fuel tank. My concerns are is it safe to put another fuel tank in the engine compartment, if so would plastic be better than aluminum? Of course either will be vented to the outside. I'm thinking of a 25-30 gal tank. Any thoughts/input?