I don't think a pressure gauge is of any value with a propane tank.  A
pressure gauge is useful with a compressed gas, but not a liquified gas. 
With a liquified gas, the pressure will remain constant as long as there is
liquid in the tank-in other words, the gauge will read the same until the
tank is nearly empty.  I know that big RV's have propane monitors, but I
don't know how they work (weight? float and sending unit?).  The EV Winnie
has a gauge, but it is clearly not a pressure gauge, and I was never able
to figure out how to read it.  Surely somebody out there knows how these
things work?

Bill
87 camper.