I just finished riveting the tail-cone section of my Mustang II. One thing I keep noticing on more and more metal airplanes is the way the sheet metal has been dented by the force of the rivet gun, from the outside, on the curves of the fuselage. I just spent about four hours inside the tail-cone "back-riveting". It came out simply beautiful. If you want to eliminate those unsightly dimples in the skins, practice your back-riveting, get a good helper (Mine is an RV6A builder) and do as much as you can from the inside. I use rivet tape or 3M masking tape over the tops of the flush rivets to eliminate bucking bar or rivet set marks on the skins and rivet heads. Back riveting takes a little practice, but the results are well worth the effort.