Wire routing

[B_K]

I'm no expert but if I remember correctly condensation self generates as temperatures rise and fall.
So that is why I believe putting the conduit inside the A/C ducts is going to produce condensation.

But again I'm not a HVAC person, but I did stay in a Holiday Inn Express once.
  BK 

[Debo]

I did one of two things. Thing #1 was to take the cable/wire down through the floor and traverse the distance in the bays, then come back up through the floor. It requires drilling a hole and using a grommet in the bulkheads that separate the bays, but they're aluminum and are easily drilled. Thing #2 was that above my windows, I built window valences that have a space behind them. In a lot of places, this acts as a wire chase where I can go the entire length of the bus. In some spots, I've installed LED lighting that's directed upward and reflects off of the ceiling, producing a nice, soft light. In one or two really tricky spots, I actually ran conduit so that the wire would have its own protected run. I probably overbuilt my electrical system with regard to wire sizing and chafe protection, etc, but I REALLY don't want to ever deal with a fire on board.