The problem with snow tires on an expedite vehicle is that we spend virtually no time driving in conditions that require them. Snow tires are made so that they are softer and more flexible in colder temperatures, and will give you a much better grip on icy and snowy surfaces, but because of the softer composition the treadwear just sux on otherwise dry pavement. Ninety-five percent of our miles happen on primary roads, roads that are quickly cleared of snow, roads that have that otherwise dry pavement. You may be in conditions one day where snow tires would be preferable, but the next day the roads are clear. For that matter, the next day you could be in Houston or Savannah or Birmingham, and it might be 3 or 4 weeks again before you have another day where snow tires might be preferable. On those half a dozen days a year where you need snow tires, just drive a little more carefully and smartly and you'll be fine.
Of course, if you're one of those drivers who prefers to hang out in the midwest and always feel the insatiable need to get back to the freight lanes, then you might want to consider snow tires. If so, do it up right and get 4 of them. Snow tires, or aggressive tread tires, on the rear only does very little to help with the problems of steering in snowy and icy conditions. Having snow tires on the rear for the purposes of getting started and for acceleration is great, but it's meaningless if you don't have the proper grip on the steers while you're going down the road. Basically, if you can get buy without snow tires on the front, then you don't need them on the rear, either, and if you really and truly need them on one or the other, you need them on both. If you need them, buy four snow tires and then go to a junk yard or eBay and buy four spare wheels on which to mount them, making swapping them out a relative snap.