I don't know what policies the bases follow, but here in So Cal we get alot of snow-birds that start coming in sometime in October/November and stay all winter. So if there were to be a major problem, available space would be it. I work for the Bureau of Land Management and we have Long Term Visitor Area (LTVA's) that you can stay all winter for less than $200. Of course they are dry camps, but there are vendors that bring fresh water and pump septic tanks, sell propane, etc. and town isn't all that far away anyway. But southern states are popular in winter, so I'd imagine those bases see alot of action.
