My take: My 87 was the family daily driver for 15yrs in Southern Michigan. I washed it every week both outside and undercarriage all the time. The dealer had sprayed on a tar like substance that really did a good job for so many years. After I took it all off via blasting there was no rust on the body and only surface on the frame. I've sprayed every crevice on all body joints as well inside the frame rails (hundreds of holes) with CorrossionX (a Mil Spec) spray. Although I live in Central TX and haven't driven the car in the rain since the off frame, this stuff flowed well into the crevices and leaked all over the floor from the heavy spray applied. Don't know if it is good or not. For the rust belt guys: Wash, wash, wash underneath is the best you can do. Stay out of puddles (salt baths) Pic your favorite brand and apply liberally!