Hi mrwhite, how much info can you handle?
I'm an avid camper, and shoot on crown land.
Will you be camping with wee ones, and do you have 4x4?
I like the east side of Harrison, it's where my "go to" is. There's a couple spots at 24km, lots at 30, couple between 32-34, lots more at my favorite, Silver Creek 34km, from there to 40 is few and far between if you want to camp near water.
West side of Harrison, not much near water until 40km, nice big beach. A few more spots along the way.
Chehalis Lake NE is still Crown, access from Harrison West 28km. Clean road other than one spot, but cars still get through.
Chehalis Lake south end has a couple spots. I don't remember km marker for turn off but google earth will help.
Hale Creek, Harrison west 26km?? is still free. North entrance closed to logging South is a really tough road. Beach and bush camping.
Salsbury Lk, Sylevster Rd. If you have a canoe you can camp on the island. Park at 12km main road, 50yd hike in.
Kenyon Lk, Sylvester top of mountain, another hard road. Again, canoe to the island.
Sadly we lose more and more places each year. Wasn't long ago and everything on Harrison and Chehalis was free camping. All these spots fill up quick. Lots of groups on long weekends. May long, I saw over 200 people in what usually holds 30. I usually leave Maple Ridge by 6:00pm Friday evenings, and I've always found a place to go. Without 4x4 you won't be as lucky.
I've shot at most of these places but usually leave camp a couple km's.
If you're ok not having a lake/river/stream, drive up any of those roads and you find 1,000 spots.
Side note for anyone camping near a river, don't let it sneak up on you. I've gone to bed with 5' of dry bank and woken with water 6" away.