It looks like the source is where the outboard motor control cables pass through
in the cockpit foot well wall. There was just an open hole there and the rain was getting in.
That ought to be easy to fix. It just needs a cover that will keep the rain out instead of funneling it into the locker.
But where would that come from?
Who has the right size and shape in stock?
I couldn't find exactly what I thought I needed, so I decided to bite the bullet and make it instead.
This picture is the end result. Just a small cover to divert the rain water away from the hole in the wall.
This was made in one afternoon and evening - hand laid fiberglass...
Use your imagination!
This one is a soda bottle (filled with water to hold shape)
Three layers of glass cloth were laid on and wet out with West epoxy.
West System has a lot of information on how to mix and use their resins
as well as safety precautions.
Read the books and follow the directions.
It's not complicated, but mix ratios are important - so get it right!