Whenever I repaint outdoor door trim I like to strip off all of the old paint down to the bare wood. After I get the trim down to the bare wood I will fill in any cracks or deep scratches with a wood filler that can be used for exterior purposes. The product that I am currently using around my household is Elmer's Wood Filler. After applying the wood filler and allowing ample time to dry I will sand the entire door trim smooth to the touch with sandpaper. Using a wood filler product results in a professional appearance after the trim has been and painted, although I am far from a professional.
It does not take very much wood filler to fill in door trim gaps. The container of Elmer's Wood Filler that I own has lasted for well over a year. I keep the lid secured tight. I have used wood filler from the same container for multiple projects. I have not had any problems with the wood filler maintaining its integrity. The product does not bleed through any surface that I have painted so it is impossible to tell where the wood filler has been applied. Elmore's Wood Filler is easy to apply and sand. I am satisfied with the results and will not hesitate to buy more of this product.