The good news is once past the campground and up on the BRP, the temps and humidity is a lot less than down in Marion. Most folks will probably be by the campground while the temps are still in the 70's. Just be prepared for the humidity to hit you in the face after you've finished when you come back down off the top of Mitchell to the Campground.........But you are exactly right-hydrate regularly along the way and with some electrolytes. Really bad incident several years ago with a female that drank just water-and way, way too much of it.