No, not theory, but factory standards.
Even on new trailer I did not smell propane, each time I was restarting it after 5 days, not only propane lines had no pressure, but were filled up with air.
Bleeding long lines with restarting refrigerator 20 times was pretty annoying.
Still the system passed reinspection.
My present camper has steel pipes outside and copper tubings inside, still when I turn the tanks off, the pressure indicator will go to red in matter of minutes.
Rubber hoses at the tank are my biggest suspect.