The problem I see with an oven is the seal. They are not made to hold temperature like refrigerator seals.

Here is my life experience and you can test it out if you wish....

I live in FL and we lose power frequently here for various reasons. My freezer portion of my refrigerator will keep food frozen for 3-4 days without power and the refrigerator section will keep food cool enough to prevent it from spoiling for longer than that. My little wine cooler incubator will lose less than 1F starting from 90F over 4 hours without power.

My oven however will not hold temperature and is nearly down to ambient in an hour without power..... heat your oven to 325F and throw a roast in it. Now shut your main breaker off. Tell me if that roast cooks at all? Your food will still be frozen tomorrow......

My little wine cooler construction is on my website and I am currently building a full size fridge incubator. The room will be needed this year with the amount of clutches expected. Only the heat tape is installed and wired. Fan installation is next and then all that is needed is a rheostat for the fans and a thermostat. It still works and has not been stripped. I can still move it without any help. It will hold more clutches than an oven, and best of all it was FREE!

I am not using the glass shelves. I want more airflow and the glass will block that.

Progress so far (not very exciting):