Bacpacjac,
I haven't hiked that route, but I spent my formative years (in the outdoor sense) in Oregon and Washington. For the last three decades I've lived in Alaska, and have spent a lot of time hiking, camping, and sea kayaking in coastal areas. I'll give you my thoughts on coastal camping. First off, assume you and all your gear will get thoroughly wet. Maybe you will get lucky and have good weather, but assume the worst, plan for it, and things can only get better!
I find when I'm hiking in the rain I'm better off just getting wet and not worrying about it. I find wet pants, or especially rain pants over wet pants to be be very constricting and tiring. When carrying a big pack I'm usually putting out a lot of heat and don't have a problem staying warm while hiking. Hence, unless it is very cold, I will often hike in just shorts and a light synthetic top. If it is windy I might add a goretex top, with front zip and pit zips open. I keep my other clothes dry until I stop in shelter. Do have good raingear however, for when you are hanging around camp, or when the weather gets really severe.
EDIT: Forgot to mention that I do like to wear a good rain hat while hiking in these conditions. I like the
Outdoor Research Seattle Sombrero. It keeps the rain off my glasses and somewhat keeps it from running down my neck! The only time the Seattle Sombrero doesn't work well is when it is really windy (the brim flops around too much). So I also usually carry a simple baseball hat, which doesn't keeps the rain off so well but works better in the wind.
Don't assume your pack will keep stuff dry. Put all important stuff (sleeping gear, extra clothes, etc) in waterproof bags inside your pack. There are some new waterproof stuff sacks (silnylon and other miracle material) that are very light weight and very effective. A cheaper but still effective method is to use plastic garbage bags.
Besides a good tent, consider carrying a small lightweight tarp (silnylon or similar). You can use this to rig a quick small shelter to eat lunch under while hiking, and for cooking outside your tent. You can also rig the tarp to make sort of a porch at the entrance to your tent. This gives you a place to get out of the rain and take off your wet gear before getting into the tent, which helps to keep the inside of the tent much dryer.
Extended wet periods in coastal areas are often due to a whole series of weather fronts passing through, one after another. In this kind of a pattern your gear will get damper and damper, not matter how careful you are. The good news is that often there are short breaks with even a bit of sunshine between fronts. These breaks may last from a few minutes to a couple of hours. Take advantage of them to dry your gear. Keep a length of cord handy to rig an improvised clothes line. When the sun comes out, stop, take a break, and hang up wet gear. Even a few minutes of sunshine helps to dry stuff.
I've heard that coastal route is a really beautiful trip. Have fun, and don't let a little dampness get you down!