I use a chest freezer with a Brewpad heating element stuck to the inside wall (for warmer fermentations/bottle conditioning), and a single-stage Johnson controller. Since getting this, I haven't used the freezer's compressor to cool the chamber, only the heating element, as ambient temps in my basement have been in the low 60's, and I haven't done any lagers or overly cold fermentations (yet). I have my temp controller probe taped to the outside of an Ale Pail/carboy, insulated by scrap styrofoam. However, since we had a non-winter in Maryland and it is getting warmer, my basement is now right around 70 degrees. 

I switched the jumpers on my controller to a 'cooling' setup ("cut-out at setpoint"). Just last night, I made an extract stout that I want to ferment at 67 degrees. After getting the temperature inside the chest to around 67, I taped the probe onto the fermenter and went to bed. checked this morning and both the ambient temp of the freezer and the fermenter read 67 degrees. However, I went home for lunch, and the ambient temp was down to 58 degrees (!), with the fermenter temp holding at 68. My question is, with huge swings like this, won't the ambient temp ultimately bring down the fermenter temp even if the controller is 'not trying to', when the walls of the freezer are cold from the compressor, and the chest is sealed shut and providing insulation?

I understand that fermentation (active signs this morning and this afternoon) can create some decent heat from the anaerobic reactions, but is there a way to control this to a greater extent, or does it matter?

My other question is how/if anyone manages moisture inside a chest freezer fermentation chamber set up. Even with minimal compressor activity, it has kicked up quite a bit of humidity inside.

Thanks!