If the lines appear OK, you need a manometer to check you have at least 11 inches of water pressure after the LP regulator. This link will show how to construct a manometer:
If you type "manometer" into the search box at the top of the screen, you will get 14 hits describing the use of this simple tool.
Another thing to check is that there is no liquid in the flexible tubes by the gas tanks. The tubes should run upwards from the tanks to the regulator, not down, as on many Airstreams. The liquid drying agents in the tank can run down and fill the regulator in this case.
If the pressure measured by the manometer is too low, you will need to buy a new regulator.