Which trim tabs and what size?

Would like to install trim tabs on my '91 V-20. I need some help making the choice between electric and hydraulic and what size I would need. Thanks

[Franco]

A LOT OF FOLKS SAY HYDRALIC TRIM TABS LEAK FLUID OFTEN, CORROSION MAY BE A FACTOR WITH ELECTRIC. I HAVE A SET OF THE NEW VOLVO QL SERIES TABD THAT ARE ELECTRIC - THE FLUSH MOUNT ON THE TRANSOM AND HAVE A BLADE THAT EXTENDS DOWN VERTICALLY INSTEAD OF BEING A HORIZONTAL EXTENSION ON THE TRANSOM. PRELIMINARY OPINION IS GOOD. I BOUGHT THEM FOR MY NEW BOAT BUT CANT USE THEN DUE TO THE HULL BEING FOAM FILLED SO I CANNOT ACCES SPACE FOR THE WIRING HARNESS - CHECK THIS LINK
http://www.foreandaftmarine.com/VO-QL3841717.htm