It can be the hoses, Tank fitting, connections or a regulator.
In my case it is the Red step-down regulator on the passenger side of the Propane lockers.
Not good when you wake up to the foul odor of Propane and do not know where it is coming from. As in any troubleshooting, start with the basics. I shut off all, or in this case both tanks, let it sit for an hour with all doors open (Propane locker and 'Garage' doors)
No smell anywhere, Then opened just one tank, in this case the Passenger side. Make leak check solution in a small Tupperware container with dish soap diluted a bit with water, got one of our Leather Dye applicators we use in our Leather business, but you can use a small rag and dob it on. Got lucky and found it coming from the weep hole in the Red step-down regulator, it was really coming out hard. If I wasn't deaf, I probably could have heard it.
Shut down the tank, removed the flare fitting attached to the 'Pigtail', then using a back-up wrench on the gas line, took off the regulator, drove to a RV Parts dealer here in Roswell. (Right behind the wrecked Saucer from mars..)
They cost around $7.00, I paid $18.00 Typical.. but was glad to get it. The original Red regulators were stepped down to 7# or so, the new ones are 25#, they said they don't make the lower pressure regulators anymore.
Your leaks will typically be a hose, a tank or a regulator, rare the fittings will just start leaking.
Went in to excruciating detail on this to help those who are not too handy, the mechanically inclined folks have already dozed off by now...
https://picasaweb.google.com/Jimsue1...eat=directlink
This does not cover everything it can be just the stuff I can remember on my first cup of coffee.
As in anything that may blow up or catch on fire, get an authorized competent RV repair service to do it if you know you might mess it up.
BTW, on gas, I never use Teflon tape, in my 40 so years of repairing HVAC systems I have seen too many gas valves with Teflon tape caught in the intake screen, and it doesn't take much to clog the little orifices in regulators. I use Pipe dope, Rectorseal brand, or the Blue Locktite in a tube I always carry..