Conduit is an excellent solution, and don't discount those cable trays. My boat
was built with cable trays on the inside of the lockers in the main cabin
. An excellent solution. It also has lot of conduit. And real PVC conduit is a whole lot easier to work
with than waterpipe. Thinner and lighter and much more flexible.
For conduit, make them at least
twice as big as you think you need. Boat
wires multiply. At EACH end of EVERY conduit label EVERY wire. Be sure to leave a length of string in each conduit so you can pull that next wire through without a hassle.
Helter-skelter spaghetti is a nightmare. rip that crap out and do it right.
Lastly, boat wire is VERY different than Romex, although they have superficial similarities. Boat wire is more expensive, but is really worth it both in the long and the short run. Boat wire needs to be flexible, so it has lots of very fine strands of copper. It needs insulation
that has a high temperature rating, and is water
proof. The best has the individual strands tinned for corrosion
protection and better connections.