First time I ran into this, there was a ceiling fan on the roof of the porch. To top it off it certainly didn’t look like an exterior grade fan. I taped it off and used plastic, then double wrapped it to be sure. From the junction in the roof line to the fan motor itself, it looked like it had separated a little bit and there were gaps. What I do, and who knows if it is right but it works, I rip open some of the plastic to make a hole, then tape the hole down to the surface so it doesn’t billow out while working.
So how do you handle this pro washers? I imagine down south these things are as common as heat in the summer.