Not 100% sure, but I think the battery pack is encased in aluminum. Much of the rest of the undercarriage will be aluminum from the body, and most of the major suspension parts are aluminum, so no issues there with salt corrosion. The motor casing is likely stainless steel.
A spray from a hose should be plenty to remove road salt. Give it a good blast in each wheel well and under the body, particularly around back by the motor, and you should be fine.