I am new to the pellet grill myself ........ that said. I don't see a direct flame that could cause a flare-up. Coal & gas grills have an exposed flame.
You have cleaned the grill, so you have seen, below the flavor bar.
#7 heat source burning pellets contained.
#6 heat defuser, distribution
Frankly, I cannot see a way any drippings could or can cause a flare-up
The pellets are hot, burning ambers. So, no flame, you've used a charcoal grill? After the coals look white, no flame. If you blow air on them, they get red and hotter.
The pellets are the white coal, and a fan blows air over them. The fan air volume increases & decreases, regulating the heat as the pellets are added.
That is taking place inside of part #7.
Rain ....... I would not leave my grill cooking in a rainstorm ..... think about it.
Pep