where to put the oil tank?

[Capt Terry]

One man's solution that has worked well for many years. In 1985 when I added a tank for my Merc 150 to my '76 20' Seafari I put an access hole in the motor well and made and mounted a fiberglass tray (glassed 3/4" plywood with borders) then attached it to the keel on one side and the hull or stringer on the other side with resin and cabosil cement. My tiedowns were heavy duty bungees with stainless hooks which I replaced whenever they got soft and stretchy. Although I would have preferred not putting the weight in the stern, it seemed a logical location and on the portside it helped offset the weight of the two batteries on the starboard side about the same fore-aft location.
In 2013 the dealer used the same tray when he added a smaller tank for my ETEC 150 HO (the lightest 150 I could find), thereby picking up 43 lbs of additional engine weight- oh well. Most of us weigh more than years ago too!