No heating them up should not cause condensation.
Condensation is caused by cold not heat. The relative humidity is relative because warm air holds more molecules of water than cold air. Thus as you cool air it condenses and you get rain, fog, snow frost etc... Anyway so heating your harddrives should be fine unless they are covered in frost and you heat them it melts and condenses on the motherboard or something.
Look at a psychometric chart to see what I mean