We carry grocery sacks to wrap our feet in on this ride. That way your shoes stay mostly dry. I have never gotten drenched on this ride, but I have gotten wet. I plan to ride it next week, even if I have to wear a poncho to do it.
The wettest I have ever been on one of these rides was the one at AK in WDW. I had to go in the bathroom and wring my clothes out. But the one at the local park here has a waterfall that the boat passes under and the boat spins right as you pass under it so everyone on the boat gets pretty wet. At least GRR doesn't have one of those.