cure it with a handheld UV flashlight, and then sand it smooth. Essentially it’s like using resin in place of a body filler like Bondo, with the advantage here being that the resin cures in seconds.

Other UV resins should work similarly from what I understand, but I haven’t tested them. Sanding, usually along with using fillers like Bondo Smoothing with solvents (e.g. acetone vapor bath for ...