A few suggestions:
Head up the pch to the Bay area (can't offer suggestions on where to stay)
Then head up 101, stay in the Redwoods...you can actually go camp on the beach in that area, plenty of room if you can find a place
http://www.nps.gov/redw/planyourvisit/campgrounds.htm
Then head up further north, stay somewhere near Tillamook, great area, lots of stuff to do (not sure if that fits your 400 mile rule
![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
You could hit the Dunes, where you can camp on the beach...
Then hit Gerhart, Oregon, near Astoria, camp on the beach, have a big fire, lots of stuff to see (near Astoria and the big lighthouse, they just had a Goonies 25th anniversary there)
Further up the 101, you can stay in Long Beach (near mouth of the Columbia, big long spit, if you want you can cheat and camp at the end of the spit, but might get in trouble) great sunrise over the water there
Keep driving up 101, hit the Olympics, you can camp on the beach there, honestly though the whole Nat'l Park will be crowded, hit the Nat'l Forest instead and just spend time in the park
http://www.fs.fed.us/r6/olympic/
Stay on 101 around the Olympic Peninsula, then take the first ferry you see to Seattle - don't bother with trying the long-***** drive around puget sound, and the ferry is cool (maybe you'll see killer whales)
Hit Seattle, then head north, if you can turn right on Hwy 20 (North Cascades Hwy), plenty of places to camp up there and awesome scenery (kinda a Glacier lite)
Turn on 153, head south to 97 and Lake Chelan...and basically follow 97 all the way to Crater Lake area (southern Oregon)...then when you get to Klamath Falls, stay on 97 to head back to I-5 and the straight shot home (if you are sick of the teenage boys by now
![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
) or head down 139 to 395 for the scenic way south through Modoc, which is a great area btw, plenty of open areas, camping, and not very crowded.
If you have the time take 395 south through Reno, the Mono Lake area is amazing, lots of camping, then into Sequoia and back home...great thing about 395 is that you can 'cut over' to I-5 in lots of places depending on how much time or patience you have left...
Have to say I'm jealous of your trip, I've done the opposite a bunch (Portland-SF-Portland or Portland-LA-Portland) and if you stay away from I-5 you'll find plenty of formal and informal places to camp and the scenery will be amazing the whole way.