Check out this disaster. Here is a prime example of what not to do if you care about your car. This 70 Cuda rear quarter had the typical small pinholes and some crust but this was done by someone that was trying to band aid the thing. Trouble is that the rust is coming through the back side and what ever primer or bondo or fiberglass you apply will just give moisture a good foot hold and really rust it out that much faster. If you see pin holes the surrounding metal is surely compromised. If your taking the time to fix it that car deserves the best. Of course this is just my . JC.