I've had good luck with Blue Sea CableClams, especially replacing those little metal-capped grommet fittings (that always did leak with flat cables). With careful drilling, CableClams can handle flat and round cables
, around which they compress nicely when the collar is tightened down. What I like best is that all the plugs and connectors stay nice and dry on the inside.
I did get somewhat carried away and bought a second set so as to have spare outer collars and rubber plugs to seal the openings when the cables and mast
are pulled. (I know, that's a lot of cables. The blue-tracer line wrapped around them was courtesy of my daughter, who was busy "creating" something).
(hmmm, not sure I've gotten the hang of attaching photos... first attempt)