Best current rust preventative treatments and paint protection?

[roadster]

If driven in winter , always like to clean underside thoroughly after they salt road final time of season and a good rain to wash roads has occurred . Always thought that road treatment allowed to get into nooks and crannies and allowed to get wet all year around causes most problem . So a good bath of under carriage at self serve car wash or if you have pressure washer another way . And drive thoroughly to air dry when possible after car is in heavy rain or after good bath .