I'd flood the interior with fresh water for a few hours. You want to get the salt out to prevent future rust. Soak the seats, and block the doors' drain holes, then fill them up by pulling the rubber strip away from the bottom of the window glass, then drain and repeat one or two more times. Rain will eventually get in there but it will run straight out and not get to places the salt water got when the doors were submerged.
Once you've flooded the carpet and scooped the water out, scrub it with a brush to loosen any remaining salt, then flood it again. A wet / dry vacuum will get most of the remaining water out. I have two Ridgid vacuums from Home Depot that will suck the paint off a wall. They have outlasted all the other Shop-Vacs and Craftsman vacuums I've had. Use a fan to dry the interior to prevent mold from growing. Auto detailers regularly shampoo carpet and seat cushions. They just use fans to dry them.
The salt from the ocean air is already hard on the bodies. Here in Wisconsin, the road salt capital of the world, salt is the biggest contributor to rust. Rain water gets into the same places as the salt does, but running the car through a car wash forces that salt into places it doesn't normally get to. That has already happened to your car so washing it can only remove some trapped salt, not make it worse. In my case, my '88 Grand Caravan has never been washed since the day it was new and today it has less rust on it than many ten-year-old cars.
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Friday, November 16th, 2012 AT 8:11 PM