burlmart - As agoaliemom alludes, I would not worry about a few hours below freezing. Your choice b) should give you piece of mind. Be mindful of where you travel in the winter conditions, you stated you plan on using it all winter.
capehank - You should not have any problems with the shorter B+ units. It is all a matter of weight ratings. The one ton Chevy chassis has a 16,000 gross combined vehicle weight rating. My unit weighs right around 9,000 lbs, so it has the capability to pull a maximum of 7,000 lbs. The closer your tow weight gets to that 7,000 the slower you will go up and down hills.