How rust bleeding & galvanic corrosion is affecting on stitch welded dissimilar metals in salty atm: and how caulking can effective on this issue?

Galvanic corrosion is the most favorite in environment that you have defined. Salty atm will provide electrolyte for electron conduction and one of the dissembler metal with high rank in EMF series will starts corroding. 

Rust bleeding shows the loss of material in the form of corrosion product. It shows that the weld is losing its strength with time by loss of material.

galvanic corrosion affect the stitch welding dissimilar metals because of a low electrical current that cause oxide rust