Just to finish the story I thought I'd show what I eventually did. I made some flange adapters out of a block of plastic. Essentially a tube either side of a flange plate. There is a length of pump suction hose (green) connected to the under deck end with a jubilee clip and plenty of sealant. The flange plate then screws to the deck (with more sealant) so you won't see the green bit and the hull is sealed. The engine rigging hose the pushes onto that. Under the console where it comes up through the deck, I've put about 8" of spare hose on the top side, so the water in the console has to be deeper than that to go down the tube. Even if it does, it can't make it into the hull void.
I've run two of these, on wither side of the main central stringer. One for the engine and one for the lighting cables, co-ax, sounder cable and steering hoses.
I'm thinking about closing off the cable one with a quick squirt of expanding foam and then a cap or black silicon sealer or potting compound. It will probably need a thin tube with cap in the end though so I can let any water out by lifting the front of the boat (on the trailer).