The things can be built with screen covering the air intake and exit vent, and tight doors to keep out the bugs. During operation its not a problem-if it will dry your product, it will also dry the bugs. Storage when not in use would be when the bugs get in. Cleanliness will help, give them nothing to eat, they wont be attracted. Even if there is no food being dried, the device can be set up in the sun as if it was drying food. This would keep the bugs down for sure.
Seed the Mind, Harvest Ideas.
Willie Smits: Village Based Permaculture Approaches in Indonesia (video)