If you are already near Napa, just catch 101 at Petaluma or Santa Rosa or wherever you can get on 101 and go north all the way to Eureka. No real hard pulls and no need to go over to I5 or Hwy 20 or Hwy 299. That would just add many more miles and time to your trip. I recommend that you stay off of Hwy 1 with your RV combination, it is too narrow and tight turns. Check out the redwoods on your way, but leave the 5er somewhere if you decide to take the Avenue of the giants, just do that drive in your truck.