Here's some video for you guys to get a better feeling for what I am doing.
Still a third video coming - it's uploaded to YouTube but not processed yet.
So far, it looks like I should be able to hook the UPS to the batteries, but just not plug the inverter in to wall power. That way it doesn't ever try charging the batteries at all, it only acts as an inverter.
I am guessing the sine wave from it will be fine, but I would still like to check it.
The next big thing is to decide on what solar charge controller I want. I need one that handles 48V battery packs, and has at LEAST a 100Voc input. MPPT would be nice, as the panels can put out fairly high voltage.