As one poster mentioned above it is going to extremlely crowded in Aug. The OLY Pens. is Seattle's playground in the summer. Reservations on the weekend will be impossible. Weekday you should be ok. I prefer Ft. Flagger State Park near Port Townsend (I was there last weekend with my boat going halibut fishing).
Hoh is great if you get out and hike. Sol Duc will be crowded. Plus I really don't want to spend $18 to sit in hot water for a few hours (but my kids like it so I do it). Staircase is a great place but good luck getting in spot in there. But if you are willing to hit the gravel roads in the State owned portion of the park there are over 30 campgrounds away from everything. Over 1/2 them aren't on the maps but they are nice and secluded (mainly on the Hood Canal side). I only hit Neah Bay with my boat when the salmon are running and the few places to park/camp it can get extremly crowded and LOUD!
IMO the best time to hit the OLY Pens. for crowds and weather is in September. But you may not have that option.