This happened to me the first time I took my fifth wheel out. I looked up the code. From then on I turned on the stove and lit it. Once that was done, it did not happen again. I always wondered why the gas would leak out over time in storage. I eventually found the leak using a electronic propane/natural gas sniffer. Purchased on Amazon. It is a long story, but this will get the almost nothing leak that cannot be smelled or will not make a bubble.
https://www.amazon.com/s?k=gas+leak...FFUYT&sprefix=gas+,aps,378&ref=nb_sb_ss_i_6_4
You got to wave the thing around and increase it's sensitivity slowly. They can get really sensitive! After I fixed the leak, my pressure meter never dropped even over a month of time.