After I parked the rig the other day and shut it down, I heard a hissing sound. I looked in the generator compartment and checked all the fittings but all was fine. Went back inside and tracked it down to coming from under the transmission shifter. Had to remove the drivers seat and removed the cover.
There are a lot of wires under there! The black box with the green sticker in the center of the photo has two air lines going to it. One of the fittings had a crack in it that was leaking air. Replaced the fitting and now the tanks hold air for days. The black box is used to monitor the front/rear air tanks, sending info to the gauges and controls the low air alarms (per Monaco tech). Also found they (Monaco) didn't seal the hole going through the floor for the wires. A little expanding foam solved that problem.