If your stopping during the week, Suttle will be all but empty. The little lake near Hoodoo is actually called Big Lake:), but is notorious for massive amounts of skeeters. Been up there a couple of times and no kidding just getting out of the car and back in there must've been 1/2 dozen in the car. Down the mtn a couple miles on the right (heading west) there's a small lake that's fairly shallow, I believe it's called Lost lake. There's no CG there but we see people there on the weekends. Take road NF-835 on the right just as you approach the passing lane. There's also Cold Springs CG on hwy 242 outside Sisters. Pretty remote, never full. There's also road NF-12 (Jack Lake road) right before the Suttle lake turn in as you're coming from Sisters. You can take that road down towards Lake creek, right at the creek there's a real quick entrance to a dry camp spot. Big enough for a couple rigs.
There are some large snowmobile parking lots around Hoodoo that are camped in during the winter. Not sure if they're useable during the summer. Worth a try.