On one side of your rig you have a propane tank and the automatic change over selector/regulator. The auto selector has a lever to change which tank you are currently drawing off of. On the other side of your rig, you will have a tank and a pressure reducing valve, mine were red but that is not a definite on color. I’ve had 2 leaks over the years and both times it was that pressure reducing valve that was leaking. On the backside of that valve, there is a small hole that allows the valve to adjust to the atmosphere and the rubber diaphragm in this valve decays and allows propane to escape from this hole. If this is the culprit, the tank near this valve needs to be on and you can feel the gas blowing out. Most RV part stores carry this valve as they go bad frequently