What altitude does your problem begin at? As part of our recent home sale, the buyer hired a home inspector. He noted in his report that propane was detected at the furnace. Neither of our two detectors have ever alerted, we've never smelled it, and there has been no problem in 17 years. So he must have had a sensitive sniffer that an RV shop might not have.
Since gas expands at high altitude,( just check out a potato chip bag in our pantry or open a Coke bottle at our 8900' home,) your problem may only be detectable at high elevation, and then with proper equipment. It should not be too difficult to detect if the leak is such that you can smell it. If it's a pin hole leak in the tubing, tracing the entire length of the lines may be difficult, but the problem is most likely at a more easily reached connection.
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