This.
I'm a proponent of going ahead and investing in a used freezer/fridge and controlling it with an STC-1000 (under $20 on Amazon). You can put together a dual-temp control box for about $30. Add whatever the used freezer or fridge costs you on Craigslist. I've now got three of the things regulating the temps in my fermenter fridge, cold crash/lagering freezer. and keezer.
- Precise temperature control (measured on the fermenter bucket/carboy) that you can set and walk away. No having to replace frozen soda bottles or hoping that your swamp cooler is actually cooling enough.