Hi Mikko.
There are no additional bulkheads once you are past the one behind the daggerboard case but the space underneath the floor is limited as you can see if you look through the drain at the stern (an Endoscope attachment for your smartphone is inexpensive and makes it easy to check).
The bulkheads are marine ply I believe but coated in resin and fibreglass to make them stronger and impervious to water.
You could run the wires through electrical conduit tube to protect them either above the deck or underneath – although directing the tube through the hole in the rear bulkhead may be difficult – unless you add a larger hatch which would make the under deck storage more accessible.
I have also seen people run wires through the side deck by adding an inspection hatch to make it easier to access.