Building baseboards entirely of XPS foam (if I have read correctly) is an unusual thing to do - not many do it.Hi
Before I make a final decision, if I use 50mm XPS foam as my base board, what is the best way to attach all the wiring underneath?
I've seen people have a 3mm ply and glue the foam to that and others that have just glued to the foam to the supports.
If I go without the 3mm ply, I thought about using cable nail clips and push them straight into the foam, not sure how long that would last, maybe drop some glue on the nail before pushing them in.
I would have thought that XPS foam would be insufficiently strong to prevent sagging and would therefore require support. It's moisture absorbing and warping properties are probably not well known in the hobby. I would also suggest that 3mm ply would also be insufficient.
My suggestion would be to used tried and tested methods such as ply construction and limit the use of foam to just track-beds on top of ply.
I built my boards using 12mm ply and these have lasted 25 years, including a year of storage in a Sydney garage with extremes of temperature from -5 to +40, with no impact whatsoever.
Using foam, you also need to consider how you are going to attach everything on top of it - some glues destroy polystyrene and it probably won't hold any kind of pinning.
With regards cabling, I would recommend just cutting slots like I did in the cork that I use: https://modelrailways.online/Pages/Vu/PowerFeedingwithDroppers
Run the cable through holes in the surface and do all your cable runs underneath.
Please don't bury cables in scenery: as sure as night follows day, you will need access to it. Better to access it from under the board than to have to destroy scenery to get access.
Something else to watch: some foams have chemical reactions with the shielding on cables, causing the latter to break down and short. I would suggest that XPS is a bit too much of an unknown for me to be comfortable with it.