Yesterday, I looked in the hopper and there was only 2-4 pounds (guesstimating) of pellets left, so I let them burn at 350* for a couple of hours.
When it was almost emptied, I saw several expanded pellets which led me to believe moisture was getting in at the bottom (never saw any expanded pellets toward the top of the hopper and I regularly ran my hand or a cooking tool to check for bridging).
Lots of sawdust too. I took a clean paint brush and swept down the sides and seams, as I was planning on using the red RTV caulk as a precaution (per okie smokie's suggestion).
Good thing I did this, as I looked on the outside of the joints where the auger tube and hopper meet and saw piles of sawdust on either side. This must have been where moisture, and probably some rain, got in and wet the pellets from earlier cooks.
I went ahead and sealed the seams (see pic).
On the bright side, the fan adjustments made a significant impact on ash volume in burn pot...there was very little compared to prior to the adjustments. Between this and having dry pellets, it should be smooth sailing. Of course, I'll update here if anything doesn't go as expected.
BTW, I reached out to the manufacturer and reported what I observed and how I caulked the hopper seams. He told me that the last run of their Kansas City Grills all had the red RTV caulk applied to the hopper. The Eco did not as they were manufactured prior to the changes they made withe Kansas City line. At least they are aware of this problem, and I hope this becomes standard on future productions of this grill.