Golden Rod makes some of the best units out there. I've been using them for years.
How does GoldenRod® work?
GoldenRod® heats to a surface temperature of less than 150 degrees (which is almost too warm to hold) and circulates warm, dry air throughout an enclosure on a 24 hour basis. This increases the temperature of the air inside to several degrees above the ambient outside temperature. Expansion of the heated air forces the moist air outside through the vents or loose fitting doors leaving the dry air inside. In order to work correctly, it is important to ensure that there is adequate ventilation.