Propane problem

[wingnut60]

Another nagging problem I have is occasional propane smell in the trailer--usually not enough to set off the alarm. It always occurs when the tanks are low. I have replaced the regulator, and checked every line connection with bubble solution for leaks--none found. I also replaced the original detector with a new one. I could not get into the furnace area--yet. Also, when the tanks are getting low, the center burner on the stove will burn yellow, yet the 2 rear burners work normally. The system was checked by CW about 18 months ago and pronounced leakfree.
I am at a loss to figure this out--even when the tanks get low, there should be no way for propane to escape the system?
Right now, I have both tanks full and everything is working fine. It is worrisome to not know if I have a safety problem that may be serious if I can't get it figured out.
Any ideas from you experienced campers?
I have really been helped by all the suggestions from the Forum--impressive--and thanks.
Joe