How long before damp-rid typically needs to be changed out if you have your controller set to about 64F? (Not that a couple degrees is going to make any difference...)
It is more about the humidity where you live - the damprid dries out the air, preventing condensation. The more you are in and out of the freezer, the more often you're going to have to change it out. I got the ones that have a little strainer that sits in a container, so as it absorbs water and dissolves it drips to the bottom. When it is gone, you dump the water, refill with more damprid, and stick it back in the freezer. Mine can easily go a couple of months without being replaced, but I don't get into the freezer that often, I'm just swapping out kegs. When I ferment in the one freezer I have to replace the damprid more often, because that raised the humidity in there.