I use a 15hp 2 stroke kicker on my 19ft aluminum center console boat. I use a 3 gal tank on the deck at the back of the boat and I made a "box" to cover it and keep it out of the direct sunlight. I have never used more than roughly half that tank of gas in a single fishing trip. The kicker is quiet and uses much less fuel, and like many other have mentioned, I like the security of having a 2nd motor on my boat.
Forgot to mention that I had to add a pre-set throttle assembly, Evinrude part # 174741. Without it, my motor wouldn't hold its speed above idle. It would fall from 2.5 mph back down to idle speed. Now it works like a champ and stays at whatever speed I set it at. Its a 1992 Evinrude.