Pete,
I have been debating the same thing to be able to add wiring for a battery monitor etc. I poked around underneath with an electrician snake for several hours trying to make the path across under the floor and could not find the access holes on the other side.
Separately, I had a pin-hole leak in my cold water grey pipe last year in the port salon settee (see picture of the aft section). I cut the old grey pipe and replaced with a new piece of Pex from Home Depot (3/8 ID I believe it is) and connector fittings from Plumbing Supply
https://www.plumbingsupply.com/polyb.html (the grey connectors).
The old and new pipe fit perfectly with the replacement fittings. So, I took the pipe apart again this year, taped a messenger line to one end, fed an extension pipe with duct tape and pushed the messenger line across under the floor to the galley sink cabinet, with a friend pushing the pipe as I pulled. Once I had the messenger line secure, we reversed the process and put the existing pipe back in place. It went very easy.
Now I have a messenger line to pull any electric wire across under the floor, Worked like a charm. (Take another messenger line along with the wire on the pull, so the next time you need another wire, you have the next messenger in place for the next pull .