Replacement or repaired body panels may require additional efforts to restore the corrosion protection on the panel backside by using an epoxy or 2k primer that has been tinted to replicate the OEM appearance. In addition, the backside may have a unique overspray appearance. Additional labor and material for backside panel corrosion protection and refinishing effort is NOT INCLUDED in CCC, Mitchell and Audatex.

Honda provides an excellent example of their requirements on page 3 “Backside treatment of new panels” Corrosion Protection for Honda Vehicle Rep