Several years ago I tied up a bunch of poppers and other subsurface "flies" for use on El Salto. I carved the body out of balsa wood, embedded a hook in the lower body and filled it over with wood filler. After sanding, I spray painted a base coat on the popper. After drying, I wrapped the fly with material know as "bridal vail" and sprayed it again with a different color. When the paint dried and the bridal vail came off, whatdayaknow, my fly now had scales. Some dead animal part were then tied onto the shank of the hook, eyes painted on, and I was then the proud owner of a fly anglers version of a lipless crankbait.
My baits looked nothing like the Bog Baits. Those things are from another universe. But I bet the painting techniques were somewhat similar.