If you're planning on taking 101 to 5 via 20 through Clearlake, I would suggest Blue Lakes Campground. I have actually never stayed there with our RV (we have a mobile @ Clear Lake), but I know folks that have used this campground.
http://www.bluelakepineacres.com/. Blue Lakes before Clearlake about 30 minutes from Ukiah. It is directly on Hwy 20. It's a small park, not many spaces so I'd call in advance. Check to make sure they can accomodate your rig.
Another option is Cloverdale KOA. It's off the road a bit, great views, expensive.
http://www.winecountrykoa.com/ We have stayed there with the kids and all the amenities. Nice place...somewhat of a difficult climb into the park.
If you are a member of 1000 trails, they also have a park in Cloverdale, north of town, just off 101.
BTW, this is the route we take when going north on 5 (Seven Feathers). It is a good road, no problems towing the Monte.
Ken