Travel from Massachusetts to Florida in March, should I dewinterize here or there.

The weather in MA is too cold to de-winterize.  What if it freezes the nigh before you leave?  Why be in a hurry to de-winterize?  Are you planning on stopping for a few days on the way south? If only a few quick night stops, get a 5 gallon - or a few milk jugs of water and set in the bath tub.  This will be enough to flush the toilet and wash your hands. Then de-winterize at you leisure in the warm weather.