When I added my cylinder head temperature and air/fuel gauges I needed to run more wires from back to behind the dash. I didn't want to disturb the carpet so I ran the PVC conduit. I used elbows with removable covers to make it easier to pull wires. Currently, I have one flat multi-conductor cable in it.
I am still trying to get my cruise control to work. I selected a wireless switch so I wouldn't have to run additional wires front to back for the cruise. Typically, the wireless switch would be on the steering wheel and the receiver would be behind the dash. I have the receiver in the engine compartment. The switch does communicate over that distance when the car is not running. I don't know if the engine running caused interference or if I have some other problem.