It is very easy to check your boat LPG system. 1. With fittings connected, open you gas tank valve, 2) Turn on your gas solenoid, 3) confirm flow to your appliances, then turn them off, 4) note solenoid valve gas pressure gauge reading, 4) turn off solenoid breaker, 5) close tank valve and check gauge pressure reading over the course of 24 hours. If gas pressure reading remains steady your solenoid is doing it's job.
Check gas line and fittings: After 24 hours turn on the solenoid and observe gas pressure reading, leave appliance in off position, observe solenoid gauge reading. If gauge pressure remains constant your pipe and gas fittings are tight.