I own a Ferrups 3.0 KVA UPS.
I would remove the insides, add a hotplate on the bottom and a thermostat to maintain temperature, and close up some of the holes and add a adjustable vent.
Also I would set up racks inside. It looks like it could be done relatively easily. I have a lot of scrounged hardware for supporting racks, although I would buy new stainless steel racks for food safety reasons.
Any thoughts on this plan? Are there any fatal flaws in it? This UPS is unlikely to fetch any good money these days.
i