fish nautique transducer location

[sirfinn]

I mounted mine near by the live well pick up. bad spot! does not work at speed. Later I discovered an area just fwd of L/H transum 3' outboard of keel. looks like a previous owner had a box glassed inn and was shooting through the hull, with out a hole drilled. I have read every restoration of these classics and this one detail gets left out. any help locating my second hole appreciated.

Also, has anyone used rubber hatch seal material for the deck boxes? if so shoot some pics and details on the material and knowledge. ill try and attach some pics here.
Many thanks. I have a 76 fish nautique. Ijust spend years restoring and never use it. This is my break out year!

circled is my transducer.
Orange tape is where I believe it should be?