So John58 has offered a very good approach, i.e. a 12 volt refrigerator and build yourself a golf battery UPS. This will work and would be a nice approach for short and long (up to a couple of days) power outages, although not inexpensive.
Do you have so much insulin on hand that just having a logging thermometer wouldn’t be enough? Since insulin is pretty robust, and using a logging thermometer would help you with knowing that it was stored for x time outside of ideal storage temperatures.
Also, if your power outages aren’t prolonged, it seems that the insulin might not get that warm before the power comes back on and gets back into a more ideal storage temp.
Finally, you mention that your refrigerator cannot be powered by a UPS, that is sort of true, but if you built your own golf cart battery large UPS and used an inverter, you could power that refrigerator for quite some time.
Just a thought.