This shows that is can be done, without adding any risk.
Your GB classic, had it come from the factory with propane, Has a locker under the port front seat up top, with the tank(s) and solenoid, a drain, and is not located over an opening window. In those pre fit GBs, there is usually a valve protruding into the galley overhead, that gives you a positive (nothing beats a positive touchy, feely valve for complete confidence) shut-off. Converting your own locker will only involve sealing and a drain that is easily routed to drain to the side deck, where any propane, if there was ever a leak, being heavier than air, will find a safe pathway to the sea.
In practice, see threads on fires. You will not find any mention of fires from properly installed propane systems discussed here, as they only occur in theory, as far as I know. Alcohol is much more of a fire hazard as a cooking fuel.