It depends on your climate and how warm you keep your room. If the temperature is ideal otherwise, a ceiling fan will help with temperature uniformity. If your ambient temperatures are cool and you want to heat the bins, you really need some kind of enclosure with heat source. A cheap, quick and efficient way to do it would be to use styrofoam insulation board (4 x 8 sheets at Lowe's) that can be cut with a sharp kitchen knife and built into a giant insulated box. You will still need to deal with the temperature gradient from top to bottom, especially if your floors are cold.