I am a hobbyist who, from time to time, will tackle my own body repair. The problem I'm encountering is paint shrinkage. It usually shows up a couple of weeks after the finish is applied as sand scratches. I always use quality products, body filler, primer, and top coats, and I'm not using an excessive amount of filler. I am wondering if the application of a sealer would help. It's frustrating to go through all that work and produce a professional finish only to have sand scratches appear weeks later.