I use the barrel lid and not a webber. Last time I smoked I was curing jerky (and actively trying to find how low I could go. I use a BBQ guru to control draft. Lowest I could maintain is 160 - anything lower and the fire was sucking enough through the cracks.
Anyway, it rained during that burn, and I managed to get 1/2" of standing water on the lid - really glad I had not drilled holes in the lid, but simply screwed my smoke stack into the bung hole. fwiw, the UDS functioned flawlessly, even with 1/2" of water on the lid.