Hi Tom,
Hey, I'm only a lowly Northern Californian, but have spent a lot of time in and around Seattle, and have lived in fairly similar climates.
To be honest, there is no complete substitute for parking a car in a nice, dry garage! However, there are a few things you can do. Some ideas:
If at all possible, at least park under a carport. Even then, use a good fitting car cover to protect against any moisture etc. that gets blown in.
I'm not a big fan of using a car cover outside, with no other protection. Still, it may be better than just leaving the car entirely exposed to the elements. A cover is better than nothing, but only barely and might actually cause problems if the car is just left covered up for months or years at a time.
A car cover needs to be well-fitted and snug, to keep from flapping around and itself actually rubbing/damaging the painted surfaces. A cover can protect against rain and snow to some degree, but there is a limit. It's really most useful at keeping out dust and dirt and tree leaves. The most waterproof covers are less breathable, which leads to other problems.
Every chance you get remove the cover and invert it to dry out very thoroughly. A cover can act sort of like a tent that traps moisture that comes up from below.
Speaking of which, park on pavement, never on dirt or lawn area espcially. Moist ground gives off a lot of evaporation, which then condenses on cold metal parts and works its way into every nook and cranny of the car, even inside exhaust systems, crankcase, instruments, etc., etc. The harder and dryer the surface the car is parked upon, the better. Ground moisture can even percolate up through concrete!
Covers also need to be cleaned inside occasionally. Any grit or dust on the inner surface will scratch, dull and rub the car's paint and chrome in particular.
Drive the car as often as possible to warm up and dry things out.
Have the car undercoated or Waxoyled. This can be broadly sprayed on the underside, but some is also best done inside any enclosed body compartments and inside the frame itself. This is done by drilling access holes, spraying the rust preventative inside, then plugging the holes. Waxoyl and/or undercoating have to be applied over a clean surface, best is fresh paint. Otherwise, they may not seal well and will crack, giving moisture and rust and entry point and possibly even making matters worse.
Don't wipe off all excess grease and oil as you normally might. Let some gather around suspension joints, under the car, etc. Lube things such as hinges and linkage more frequently than usual. WD-40 is not a good long-term lubricant (it evaporates), use sprayed white lithium grease, or other even more waterproof types of grease.
Some sort of dessicant might be used inside the trunk and cockpit of the car, to help trap any ambient humidity. Some of this stuff comes in tins that can occasionally be warmed up in an oven to release the moisture they trap. Otherwise, they do become saturated with moisture and need to be replaced occasionally. Cheaper forms of dessicant are sold as kitty litter in grocery/pet stores and in nurseries as a moisture-retaining additive for planting soil. These cheaper types generally cannot be dried out and reused, though, and don't have color-changing indicators added, to show when they are saturated (like some others do).
Change brake and clutch hydraulic fluids more frequently. These attract and trap moisture, certainly more in humid environments than in dry, desert-like areas.
To protect the fuel system, use some sort of gas treatment that counteracts moisture in the lines, tank and carbs.
And, I haven't ever used one but have seen inflatable clear "bubbles" to seal up completely around cars for storage. Not sure one of these are all that useful or even possible to use out of doors.
However, there are various other kinds of temporary tent and carport-style structures, that might be worth considering (if you have a conrete slab or asphalt parking surface on which to erect it). Check out farm and ranch suppliers for these sorts of structures (where they are often cheaper than automotive vendors). Some are made of tarp materials stretched over frames, while others actually are light metal and/or fiberglass construction.
Wash the cars occasionally, including underneath. The salt air from the Puget Sound and the Pacific Ocean is great to breathe ourselves, but not particularly kind to metal and car parts. Of course, there is no substitute for a good waxing and polishing occasionally. Especially work to seal up all chrome well, since it's actually quite porous. (Personally I like Mother's waxes, polishes and sealers, but there are many good brands out there.)
Electrical grounds and connections will probably tend to corrode more quickly, use a dielectric grease to help prevent that and to seal out moisture. Any mechanical switch mechanisms can also get internal corrosion, to help solve that look for a product called "Color TV Tuner Cleaner and Lubricant" in spray cans, found at Radio Shack and other electronic stores.
Another crazy sounding solution... Live (and park your cars) in or near Port Townsend, across Puget Sound from Seattle. There are ferries to all the outlying towns, which are pretty convenient in many cases. Port Townsend gets an average of about 15" of rain per year, which technically qualifies as a "desert"! This is because the Olympic mountain range on the Peninsula sort of shields and protects Port Townsend from incoming storms. By comparison, some areas and towns on the oceanward side of the Olympic Peninsula get around 160" of rain a year, which might qualify as a "rain forest".
Seattle itself actually gets less rain per year on average than Kansas City does. It's just that Seattle tends to get days and days of drizzle, where KC sees it all in a thunderstorm deluge now and then. Seattle is also often heavily overcast, which keeps everything from drying out very quickly (and its grey weather probably helps make Seattle the coffee house, book-reading and suicide capital of the U.S.)
There are some great short drives and areas to visit in and around Seattle. Plus, the Olympic Peninsula, San Juan Islands and many neat towns in and around Puget Sound are accessible by ferry boat. Canada is just a short drive away, offering Victoria, Vancouver and many other wonderful places to visit throughout British Columbia. I'd rank the whole area very high on any list of places for sports car driving, although it's likely you'll need the top up more often (except that if you drive fast enough, you don't get wet in the rain, or so I'm told!).
By the way, you should know how Friday Harbor, in the San Juan Islands, got it's name. When explorers were mapping it, they came across a fisherman in a small boat and hollered over to him asking, "What place is this?". He misheard the question as, "What day is this?" and answered "Friday".
Hmmm... I sound a little like the Seattle Chamber of Commerce (except for that suicide statistic). In part that's because my ex-wife's uncle managed that organization for 25 years and we used to visit he and his wife often, in their lovely home on Magnolia Hill (where there are no Magnolias, actually).
/ubbthreads/images/graemlins/cheers.gif
Hey Guest!
Hey - did you know if you click on the title of a thread it will take you to the first unread post since you last visited that thread?
but were afraid to ask: 
STOP!! Never post your email address in open forums. Bots can "harvest" your email! If you must share your email use a Private Message or use the 
smilie in place of the real @
Pretty Please - add it to our Events forum(s) and add to the calendar! >> 
