Ah, that is an idea, but the NMEA 2000 is ?? wires, the sonar is 7 and the power 2.. so thats rather alot more connectionswould it be perhaps best to wire a "waterproof deck plug" fitting and have just a short lead which you plug from that to the plotter when in use?
e.g.
I use brush seals on my dashboards to lose my VHF curly wires. You'd need to add a foam friction device behind the brush so you could push the loose cables into the brush against some slight resistance, so they don't just drop away when you remove the plotter
Cheap as chips http://www.ebay.co.uk/itm/Black-Bru...167732?hash=item33a6f15c34:g:AA4AAOSwMmBVwMu9
Come to think of it, you could have the plotter's cables coming through a piece of plywood mounted 25mm behind the brush seal, out of sight, with the cables sliding freely in the plywood's holes but the holes small enough that the plugs cant pass through. When you remove your plotter, let the cables fall down the hole till the plugs hit the plywood. The plugs will be neatly hidden just behind the "curtain" formed by the brush seal. To re-install your plotter, just "fish around" thru the brush seal and get hold of the plugs, and pull the cables . You can get 2-gang brush seals
I found a small to-mount box in Maplins, so the two looks like a good combo...