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 and
oil proof. The best has the individual strands tinned for
corrosion protection and better connections.