It can be pretty tough if you don' t know what you' re doing, and pretty time consuming. Yes it is necessary to sand to bare metal, using 36 grit will get through the paint fast and give the bondo something to stick to. If you just have minor dings on fairly flat panels, it' s not that hard. If they are deep, they need to be pulled out close to where the metal once was, if not the bondo is prone to cracking, because it' s so thick. Once you' ve filled the dent you have to sand the bondo and shape it. It is a lot of work, but since it' s for a beater, it doesn' t have to be perfect. What you might want to check into, is bringing it to a vo-tech or trade school. I think they normally do the work for free, or just the cost of materials. They would have the tools need to pull the dents and work the bondo, and it would save you the hassle. Just ab idea.