On small dings, I've been using Plastic Wood, the common stuff in hardware stores. The ugly yellow color doesn't blend in much, but it sands well, especially when using a sanding block or t-bar. Under silkspan and primer, the color is hidden. I like the way it sands and the way dope sticks to it. I used light spackle for a while, nice and light, easy to sand. But dope didn't always stick well. At times the silkspan I applied over the solid surface failled to attach. Not a problem with the ugly yellow/orange plastic wood. I've hesitated to use plastic wood as a fillet. Thought it lacked the strength to make a radius and stay put. Thought it might fatigue crack over time. Of course it is possible to make a fillet using the ugly orange yellow paste, and, after it sets up, a top coat of CA or epoxy, might keep the fillet intact. Anyone try that?