Here is your quandry, chest freezers were meant to freeze not be at fermentation temps. If i go the deep chest route (vs say a fridge or a dedicated ferm chamber) here is what i would do: install a fan to circulate air and then i would tackle the dampness/sweat buying some baking soda and putting some towels down in the bottom and rotating them out every fermentation cycle. Bottom line: there is no way to avoid mold buy a fridge to ferment in and turn that sucker in to a keezer