My situation is that I rarely have to use a motor. I sailed most of this season without one. There are occasions where it would be nice to have. Pleasant Lake is only 2 miles long and a mile wide, so I never have too far to go. I decided a trolling motor would suffice.
Next we needed power. With the battery in the back of the cockpit, balance was affected. In the cabin, it was really in the way. I wanted it amidships and near the keel. My boat is open under the cockpit seats into the cabin. Other boats are sealed off. I found a place where the battery would just fit behind the starboard berth, next to the keel. There are two styrofoam blocks in here to provide flotation.
The second block of styrofoam locks the battery in place.