If your typical solenoid clicking is missing, either the solenoid has failed, a fairly frequent occurrence, or the switch and detector has failed, also a common occurrence.
I would start by opening the connection to the solenoid, turning on the gas switch, and see if power is going to the solenoid.
If power is present, you must change the solenoid - not a hard task, but be very sure you leak test after the new one is installed. You can either use soapy water on the joint, or insert a pressure gauge (about $20 at Amazon:
https://smile.amazon.com/Propane-Ba...1&sr=8-4&keywords=propane+pressure+test+gauge). If the pressure drops when the gas switch is off and the propane tank is off, you probably have a leak.
If no power is present, check the fuse. It seldom fails.
The usual suspect is the gas switch itself. Most have a detector to see in carbon-monoxide (CO) is present and automatically shut down the propane if any is detected. These detectors detect CO when none is really present and shut down the gas flow. Often cleaning the detector with a vacuum cleaner or air will fix it. If not, repair of the swith is futile - just put in a new one.
I doubt it is the ignitor - if the gas is flowing you will smell even a small quantity.
There is a slim chance your propane tank valve is not working. The leak detector mentioned above will show you that. Leak detection is an essential component of any safe boating propane system. Spend the $20 and install it permanently on your tank just to be safe.