I used to just cover them while drying. However, since I use enamels I got tired of waiting a couple of days for it to dry, so I finally made a drying box. I used one of those plastic storage containers that we bring our models to contests in.
I built a box out of particle board, with holes in the top and in one side, for convective air flow (I covered the holes with a filter to keep dust from coming through. The box has a socket and a 60 W light bulb for heat. I turned the plastic storage container upside down, so the cover is now the base of the upper compartment. I cut out the area of the top that matches the area where I drilled the holes in the particle board box, then screwed the cover down. The container itself is then set, upside down, on the cover. I cut a one inch hole in what is now the top (was the bottom), and taped a filter over that hole, which allows air to flow through the system. Works beautifully, greatly speeds up drying and keeps dust off. Because of the slow drying time of enamels, especially gloss enamels, some such system is a real help.