Can't imagine how the weather could be better. When we rode it in July last year we still got 3 days of rain out of 5 . . . South of Forks: Bogachiel State Park, about 10 miles, is one choice, though haven't camped there - others have. Next is Kalaloch CG, but has no HB sites nor showers, and sites are often reserved. Probably less of a problem in May than in summer . . There is another campground about 3 miles south of Kalaloch but it is more primitive. There's a convenience store at Kalaloch Lodge, has enough stuff to get by on. The trading post in Queets is better but it is also about 7 miles down the road. Next stop is Lake Quinault. The walkin campground, July Creek, on the north shore was closed last year and presumably is closed this year as the sign looked rather permanent. The USFS Falls Creek CG is pretty nice and showers are a mere 1.2 miles away. Since we made the trip last year perhaps you should visit this http://www.crazyguyonabike.com/doc/TWS
for what we experienced. There are other trip posts that have stopped at Bogachiel - suggest you check those out. Other than the long sprint from Lake Quinault to Twin Harbors, there are sufficient campgrounds to make the trip. There are also campgrounds on the coast north of Grays Harbor that we did not check out but have been listed in other resources. Suggest you also look at the bible, Bicycling the Pacific Coast. FYI, the ferry across Grays Harbor is not functional. Overall though, it is a pretty trip. Good luck.