I've never timed the duty cycle of my home feezer, but it seems to run a minute or two, then it shuts off for quite a while (as long as the door is shut). If yours is designed for a similar duty cycle, I believe you will be unhappy with how quickly it is damaged by running it for 3 hours at a time.

I don't know what building code restrictions you have to struggle against, or what resources you have available, but a wine cellar is a very good idea if you keep 300 bottles. During a power failure, the masonry walls (like in "The Cask of Amontillado) will act as a heat leveling sponge against the cool earth, until your system (or the city) can get the power back up.

If your only wine cooling is an open freezer and it fails, you will have to buy something new anyways in this summer heat. Sell the most valuable bottles and build something lasting, or "maybe" lose them all...