Slinging Bondo
Anyone who tells you that Bondo has no place on a quality repair job has never done bodywork. Even the best metalsmiths will use plastic repair media to skim-coat sheetmetal to give it that mirror-smooth look. In this case, we first eliminated all rust then pulled all the large dents and finished by working them with a hammer and dolly. With that done, they mixed up some 3M Lightweight Body Filler to fill in the little dings that were too small for hammer work.
The first step is to identify the problem areas. El Caminos have huge slabs for rear quarter panels, and they're breeding grounds for parking-lot dings and minor dents along the body lines. Running your hand slowly over the panel will identify high and low spots that need attention. | 
After application of the first skim coat of plastic filler, sand in opposite 45-degree angles to prevent creating trenches with the sanding blocks. Use 150-grit sandpaper with a long sanding block to create a smooth finish. After a second skim coat, we used black enamel spray paint as a guidecoat. The black paint will indicate low spots that will need more sanding. |
If you want to push the job a little faster, you can hit the first skim coat of Bondo with a DA using 150-grit sandpaper. | 
After short sessions with the sanding blocks, your hands are the best detectors of remaining low spots or wrinkles. |
The arrow indicates a low spot in the Bondo that will need attention. If there is sufficient thickness, this can be sanded flat. If not, a very thin application of Bondo will fill the void. | 
The '65 El Camino also has a distinct crease or body line that extends the length of the rear quarter-panels. Plastic filler can hide this line, so place a strip of 3M blue tape just above the top of the crease as a guide. Then sand up from the bottom to this line. Then apply another line of tape on the bottom edge of the line and sand down from the top. This technique will return the body line to the quarter-panel. |