It's easier to look at the gauge on the tank, assuming it's halfway accessible. This often will have a little black blob thingy with wires that partly obscures it; that blob is the sender for the indicator inside the motorhome. At least on my Coachmen motorhome, the gauge on the tank is pretty accessible, being next to the fill port and shut-off valve and so forth behind a door on the motorhome skirting.
Unlike the sensors for the other tank levels, the sender for the propane is usually an actual variable resistor arrangement so it should be entirely possible to rig up a more precise gauge than the little light panel. (The water tank sensors are just contacts spaced in the tank, so you can't get any more precision out of them without changing out the entire system.)