I've done the California trip down Interstate 5 and 99 a bunch of times.  I go via 395 if I have a little extra time this time of the year..But the "rest  stop" sleeping method does work ok on the interstate, too.  I prefer 'informal' rest stops..there are many truck stops, cafes, gas stations and Wal Mart parking lots that are usually a bit less "transient" than  the actual interstate stops.  Wal Mart seems to allow RVs to park overnight everywhere and they are ubiquitous.  They also often have a coffee shop inside.  I try to purchase some forgotten items from them after spending a night there..

  When I travel into urban areas, or overnight in 'iffy' suburban settings, I am glad I have along (usually) my large male Chesepeake Bay retriever and my 357magnum.  Only once in 40 years of roadside camping have I ever needed the pistol.  One time, when on the way through Texas to windsurf at Corpus Christy, some idiot climbed up onto the top of my van  while I was overnighting at a highway rest stop..probably looking to take a bicycle or a sailboard..Dunno what he was thinking..climbing onto a van in a rest  stop out of town..Had to know someone was probably sleeping inside there...
  I simply hollared out from my bed, "Get the ---- off my roof, or I will blow you off!  Listen carefully and you will hear my Dan Wesson  44magnum  (Dirty Harry was being shown at the time) being cocked"..which I did, he did, and the next sound was "feet beating" as he ran off...
  There is a nice campground near Grants Pass, right on the Rogue River  just off I-5..My favorite Wal Mart is in Willows, Ca..just north of Sacramento.  
  Don Hanson