I had a problem with really high humidity in my sump area, as it's completely enclosed, and of course high humidity in the room - I wanted better CO2/O2 exchange through it due to pH fluctuation, so I added these fans to both sides:
http://www.jlaquatics.com/phpstore/s...t_ID=cv-sfan04
The humidity on the inside and outside thing is a little tough, and probably non-existent because it's not one of those problems a majority of people have.
They do come with a heat sensor, and the fan spins faster or slower depending on the amount of heat either inside, or outside the sump area. I have one on all the time with the fan drawing air into the sump depending on the temperature inside, and I have another that draws air out depending on the temperature outside the sump.
Not sure if that helps!