http://www.autobodystore.com/

This will get you to a site that will address most if not all the issues you face in making the repair you descibe.

Making repairs to rusted panels so that you are not addressing the same issue in a relative short period of time are fairly involved.

A basic repair involves removing the rusted portion of the panel and making a weather proof repair before doing a finishing job on the repair. The best way is to have new steel or a partial panely welded into place and then using some type of filler to blend the repair to the original panel before priming and finishing the effected area.

Simply filling the rust hole with bondo or epoxy will result in the repair failing in a fairly short time. At a minimum you need to seal up the back of the hole with fiberglas cloth and resin after the rusted portion has been removed. Many times this is not feasible because of lack of access.

Randy