Yeah, Like FinS said, I picked up an old school deep freeze for like 25 bucks that had a dial that allowed me to keep the water cold enough that the minnows were barely active but at the same time wouldn't freeze the water. On top of this I bought a good Fluval Filter from the pet store, along with some water conditioner. My minnows lasted months at a time!!!
This is a pretty instense set up for somebody without electricity in thier shed, but it works like a charm!
Cheers,
UF