Summary

Connecting the various tanks and fixtures was straightforward, using automotive heater hose.  The size is referred to as 1/2", but the interior diameter is smaller than 1/2".  The hose is secured to hose barb fittings using a worm drive clamp.  The heater hose is more than adequate for the temperature and pressure in the water system. 

The only thing a little exotic is the addition of an air elimination valve, mounted at the highest point  in the system, the top water heater.  We could probably have lived without this, but...

The bathtub uses a standard Moen mixer valve, like you might have in your shower at home.

The fresh water holding tanks are vented on the top.  These six lines are connected to the vent stack for the gray water holding tank.  The tanks should not overfill, since the input is controlled with a solenoid valve and sensor system.  If that should happen to fail, excess would overflow into the holding tank until it finally starts coming out of the vent pipe on top of the truck.