Anthony:
Trim tabs are designed to push against the slip stream caused by the hull moving thru the water. If you mount the trim tab close enough to the side of the transom for the cylinder to hook up, the tab will be outside of the protective area the transom affords. As the boat's speed increases, the drag against the cylinder / tab assembly will increase. This will alter the way the water passes under the boat and put stress on the mounting plate the cylinder would be attached to. The transom is a heavily reinforced mounting surface, designed to withstand the horsepower of the primary propulsion system, what ever that is. Inboard, outboard, I/O jet drive, etc., the transom is designed to take the stress. The sides of a boat are not heavy and robust, and a mounting bracket would have to be tied in some way to the transom in order to survive with out stress cracks, etc.
I would not recommend this course of action.