I have an old 2006, and had the same complaint since I got it. Never really smell it inside, but outside. I had 'nose diagnosed' it to the furnace, and capped off the supply line to it. STILL got whiffs...sometimes..
After installing my Sturgistay, when I went around and sprayed with soapy water, I found SEVERAL loose joints in the 'hard pipe' that bubbled.

I bet they had been like that since new. I tightened them all up, and NO MORE SMELL! Not to mention my propane lasts SO much longer now.
Crawling around with some dawn and water in a spray bottle might provide some insight, or peace of mind.