Usually, when I face the beefier pokemon like Cresselia or Regigigas, that's when the rain runs out, and it has been a problem for Xurkitree in the past. I've been pretty lucky hitting Thunders outside of rain though. I've never actually considered running Brine, I mainly just use Scald for the burn chance, but it does sound like something that could work. I'll give it a shot whenever I continue the streak
I ran Politoed/Swampert in the Maison a long time ago and the opposing Tyranitars/Aurorus/Abomasnows really gave me problems. I ended up going with 0 speed IVs and a negative nature on Politoed to underspeed all other weather setters.