The manufacture states that my 2018 Sonoma has two 20# LP tanks. Does that mean gallons? On the tanks themselves it says 8.5. I am unsure what these numbers mean. At any rate it wasn't enough for a 4 ...
Light use and only 4 days with two 20# tanks doesn't sound right. My bet is that they weren't full. Is this the first time you have used these tanks? Possibly they were not "purged" and filled properly.