We spend Summers up in the Lake George area and recommend the route that Google Maps will plot for you. Take I-87 North to Queensbuty, then East on 149 to pick up 4 into Vermont. Pick up 22A North in Fair Haven to South Burlington and then I-89 South to pick up 100 into Stowe. We have run the entire route (with a 38' 5th Wheel) and it's easy and very scenic especially up through Vermont.
The Campground we would recommend would be on 149 just a short ways after you get on it at either The Lake George RV Park (http://www.lakegeorgervpark.com/) or Moose Hillock (http://moosehillock.com/). Both are very nice.