How cold does it have to be to winterize the RV?

I think it would be too risky with a whole month to go before heading south. A hard freeze could come on suddenly and compromise the integrity of your plumbing system, better safe than sorry IMHO. A few dollars of antifreeze and under a half hour of effort (many of my neighbors have it done by their preferred servicer) and you can sleep peacefully knowing chances are remote for experiencing damaged plumbing from over-exposure to frigid air. Have a great time down South.