[SCOTI]

On my 89 CC dually, my lines are routed along the inside of the driver side frame rail until the gas tank where they then go through the rail to the outside of the frame (between the gas tank & frame rail in a rubber hose).

From there the lines go into the cab under the base of the rear seat. The floor sound deadening has a 'trench' cut out so the lines are comfortably under the carpet.

They come out from under the carpet under the drivers bucket seat. My paddle valves are the basic units Ride Tech offers & are located @ the base of the seat @ the front of the seat tracks. The left side valves are the fronts (L/R) & the right side are the rears (L/R).

Where the lines go into the valves, I have them Tee'd w/1/8" airlines routed back under the carpet to the firewall where they go into the dual needle gauges.

It's all out of sight....
You don't see any airlines.
You don't see the paddle valves.
You only see the gauges if the ashtray is open.

Where the lines go through the floor, I used rubber grommets to protect the lines as well as seal the outside elements from coming in. There's also a rubber grommet where they go through the frame. Where they travel inside of the rail, I have them wrapped in the DEI heat wrap to minimize heat transfer from the exhaust (approx. 4" away @ the closest point).