I've heard good things about Brown's Bay / Ripple Rock north of Campbell River (Browns Bay - Resort, Marina & Ripple Rock RV Park - Campbell River, BC Canada - RV Park
), very scenic but you do have a several kilometer dirt logging road to navigate to get there (which can be a little rough at times, but they do grade it).
We just spent a couple days at Weir's Beach on the south part of the island (Victoria RV Resort :: Weir's Beach RV Resort :: Victoria BC
, we live 15 min from there) - very lovely, friendly staff, and right on the oceanside as well but you should call first to check availability/reservations. It can seem a little crowded in a couple spots, but we found it very quiet in the evening, very clean, and generally just an excellent place to be.
I hear lots of good things about Living Forest too, from my coworkers who frequently stay there. We'll be heading there Aug 3-7th. Also heard that Mountain Aire just south of Nanaimo is pretty good too (Welcome to Mountainaire Campground and RV Park, where we have a beautiful campground in Nanaimo, British Columbia.
), haven't stayed there yet so I can't comment personally.
On the West coast of the island, Crystal Cove Resort near Tofino looks quite nice (Crystal Cove Beach Resort: Tofino Cabin Rentals and Camping Accommodation, Vancouver Island, BC, Canada
), but we haven't stayed there yet. When we inquired a month ago they said they book up pretty quickly so I don't know how lucky you'll be.
Hope that helps!