Propane smell at furnace exhaust port

[Katdaddy]

I was winterizing my camper today. The low point drains are located near the furnace exhaust. When I went to turn on the drains I noticed a propane smell coming from the furnace exhaust port. I’ve never noticed that before. We never use the furnace, when we have power we use a space heater, when we dry camp I use a Big Buddy heater. Could I have a valve leaking and how do I check on this? 

[Katdaddy]

I ordered a small propane detector and further looked into this. The propane was only detected in the exhaust port. There was no trace in the compartment, outside the furnace, or at any of the connections. I deduced it had to be the valve leaking. I replaced the valve and problem solved.  Thanks for your suggestions and help. 

[Grit_dog]

If you don’t know how to diagnose a gas leak, take it to someone who does. 
Im more curious why you “never” use the furnace though. Especially in favor of a buddy heater pumping moisture into the camper.

[Katdaddy]

First, I know how to diagnose a gas leak. Second, I don’t use the furnace when dry camping because it drains the batteries. I was asking if anyone else had encountered this problem. I replaced the valve and the leak is gone. 
Thanks for your very helpful reply. 

[Vintage465]

Mine was leaking where the copper line tied into the furnace.  And like mentioned above use a water solution with dishwashing liquid in it.....like a cup of water to 1 tablespoon of dishwashing liquid.  Low pressure leaks sometimes take a bit to present themselves thru the soapy solution, but if it's leaking it will appearn.

[enblethen]

Could be leaking gas valve or connection in furnace. You can use soap water to check for leaks. It is low pressure so hard to see bubbles at times.

Another location, if close to propane tank is a leaking regulator.