Welcome to the forum. I'm also in Northern California and got our first TT in January. We've been to Lake Hensley and Lake Chabot with our trailer and had a blast at both - especially Lake Chabot (Anthony Chabot Campground).
If you are heading to the real North... along the coast, north of Sacramento, head over to Brookings Oregon. Harris Beach campground has got to be the best and most affordable camp ground we have ever been to. Having visited every Memorial Day and Laborday for the last 6 years, it is a much anticipated visit everytime.
Thanks for the warm welcome. Most of the time we would enjoy camping with hookups and we love camping in the woods. Coast camping is nice if the sites are sheltered from the wind. Dry camping seems reasonable if don't need the AC.
I remember camping at Brookings as a child and remember it being quite beautiful. We will probably venture there after the slide is removed on 101 in Garberville. Right now we have booked weekends for Casini Ranch, Leggitt,and Cloverdale. Looking forward to more recommendations because I have a few more weekends open this year.