Finally ran my air vent for the front grey tank.

It runs up inside the body, and exits near the roof.

I used some pex tubing and unions that were salvaged from the previous truck.

PoCo Inspired

As it exits out the top, I used a 90 degree union.
PoCo Inspired
Cut a hole in the wall, ran the threaded part outside, and cut some screen to go over the hole, and put on the fitting.

PoCo Inspired

Bead of silicone, and we were done.