First you undercoat, then you wash, then wax, then put on more wax. Then wash twice a week all winter long. That's one good reason NOT to live somewhere where they salt the roads. (I lived in Chicago for a few years and that does EAT your car alive.)
Does the salt ever dry on your car? If so is it hard to get off with soap. I've got a trick, use vinegar. Put vinegar in a spray bottle and spray it on your car, Yes on your car. Then wipe off with a wet rag and wash as normal. The vinegar takes the salt right off and will not hurt the finish. I use it on multi-million dollar yachts, and it works great. Try it some time and let me know how it works.