Any time two dissimilar metal touch electrolysis can occur. As a result, it's best to use like metals whenever possible (e.g. aluminum on aluminum). However, stainless steel will not react in the same way as most other metals under marine conditions, which is why it is the industry standard for all saltwater boats. Unfortunately, most "freshwater" boats (bass boats, etc...) are built to a much lower standard using cheap galvanized steel hardware which inevitably rusts. Save yourself the hassle and upgrade everything to stainless, marine grade if possible. Buying in bulk will help save you a few $ too. Be sure to use some 3M 5200 marine caulk on any through-hull hardware as well. Using a paint, or washer will only delay the inevitable corrosion.