Last winter reminded us that it does indeed freeze in Texas, so we are stuck with a problem - if we are getting a bunch of rain in the fall, how do we keep it over the winter to last into the spring? Aside from the same kinds of precautions I could use that we do for our palm trees (cover as best we can, keep Christmas lights on to prevent freezing) is there a way of setting up a circulation pump, similar to our pool pump, so when we would be expecting freezing temps we could circulate water from the drain/tap back through the barrels?

This is the type of system we would make. http://www.emmitsburg.net/gardens/articles/adams/audrey/water_barrel.htm

I think that is one of the best systems out there because of the height and construction. Why don't you reclaim your grey water from you house by pumping that water into your barrels from a sump pump as well as using it as a recirculation pump during the winter. You can also collect rainfall if needed. Then you are not at the mercy of rainfall at any time. JMHO Aloha