Tips on painting: 3D prints of this kind are not ' fully dense' output objects. They are comprised with 26% air by volume, which is perfect for its lightness and super-toughness. The material's properties are akin to describing it as a 'nylon balsa', and it is definitely not soft.
I found enamel paint as the base coat or primer to be most efficient method of finishing these parts. Spray cans are more suitable than airbrushing ( thicker application ), with the exception of the final finish coat . Don't try using primers.Traditional high solids primers are not as efficient in this case, as they require a lot of coating mass to build surface smoothness, and its messy. Use paint as primer, sand, and re-coat repeatedly as needed. Typically three coats can be sufficient, and a fourth for fine airbrush finishing if desired. I like 'Testors' because of its softness and semi-gloss finish when polished, and I associate it to applying solid surfacing. If ever a scratch from rough landings, handling etc., you can rub it out and re-polish. As with anything, painting adds a little weight due to the absorption of paint, but not inordinately so. All my designs are all hollow, including the fins, for the lightest of possible designs to factor for stability. Look for other paint types that behave similarly for this approach, or do your own experimentation.