Originally Posted by slimitch
Did not see an outside cutoff valve. Where is it located?
The gas valve for the furnace is located either on the side of the furnace, or immediately underneath the trailer mounted to the underbelly.
You would be wise to remove the furnace and have it "bench" torn apart, cleaned and repaired as necessary, and then bench tested.
There are some gaskets that will need to be replaced to assure that no carbon monoxide gets in the trailer.
Unless your familiar with LPG furnaces, you should seek professional assistance to help you.