Victorian
Approved Vendor : Total Composites
They are great because you can specify the runners anywhere you'd like in the ceiling, walls, etc...
I am just doing some minimal prewiring for some LED interior lights, external marker lights, and fans in the roof before installing it all together.
I'll be doing all my plumbing INSIDE the box, so 1, its all accessible to work on in case of a failure, but also to get it as warm as possible to prevent freezing.
I've seen some nifty builds with this stuff. One guy putting one on a unimog had a super long drill and hogged out a small section of the walls to run all his wires, and it came out super clean. Not the way i would do it, as it would mess with R value i am sure, but his method was nicely done.
A long drill bit, that's how it's done That Unimog owner is a Space ship engineer and did an amazing job building that rig.