4 inch hole saw to begin the installation. Wanted it mounted as far aft as possible.

Had water intrusion into the balsa core where the gas tank brackets were screwed in so I drilled those areas out with a hole saw.

Marking the spot where the transponder base will be mounted.

Notice the three holes where the bilge pump was mounted. Another potential water leak into the balsa core.

Cut into the lower area where water collects for the bilge pump and drain plug area so no puddles will form around the transponder mounting.

Spent most of the winter drying out the core with a heat gun shooting into the holes when I had spare time.

Mounted the transponder base to the bottom of the boat with a thin bead of silicone to hold it in place, fiberglass resin will be poured around it.

Undercut around the hole to give the fiberglass resin something to hold onto.

Cutting out the 3 screw holes for the bilge pump mount to screw into solid resin.

Ready to pour the fiberglass resin mixed with colloidal silica.

Resin poured.

Test fitting to make sure the transponder fits onto the base without hitting the resin.

Filling all the holes with fiberglass resin.

A whole buncha holes filled.

Sanding the deck flat.

Ready to finish the fiberglass surrounding the mount.

Used an old piece of line to ensure the shape of the cutout is somewhat the same all the way around.

Fiberglassing over the line.