When we had some very small leaks in our Elkmont 26, we considered this:
http://www.rvleaks.com/. The system puts positive air pressure inside the RV and using the exact same technique for finding leaks in your propane system, the test shows all leaks with the same bubble fluid applied to all external joints in roof, windows, doors and all joined surfaces.
TM would not pay for the test/repair ($250-$500-depending on the size and number of leaks found). They instead chose to return our TM to the dealer for leak testing and repair. Since our TM was returned we've had no leak issues.