I've been using an APC 2200 smart UPS as an inverter for a few weeks now (weekend use only). It's a 48V unit, so I'm not sure how relevant this will be to you, but it seems fine for continuous use so far, no sign of overheating even when run near max. output (2HP compressor + fridge).
I'm in Australia, this UPS has a 230 volt output, so again, it may not be relevant to your situation.
They're a bit tricky to start up as an inverter without grid power but it can be done; also, if you switch then off at the front panel when they're not grid connected they still drain the batteries, you need to unplug them or install a switch.
I plan to post on this subject in the next few days if I get the time.
Paul.