I wouldn't rely on the Bullet's "Thermal Package" to keep your RV "safe" during north eastern winters - especially if you are without hookups. The "heated" underbelly and perhaps the tanks are dependent upon the operation of the furnace producing enough heat to keep water lines and tanks from freezing. Without 110vAC and the charge produced by the converter, your present single battery will be tested to keep the furnace operating during extended periods of cold temperatures. I can't see a single battery lasting a weekend if you have the furnace on for long periods over a 3 day stretch.
Your best bet is to find a place that has hookups - especially electrical. Some hockey rinks in our area have an outside 110VAC outlet which is available for a visiting,single RV to plug in during a tournament. There might be some arenas in your area that could provide you with a similar hookup. That way, at least you could plug in a heater but that won't do much to provide heat for water lines and tanks.
It's very difficult to make your RV "winter proof" if you are boon docking. Skirting is out of the question and unless you drain all of your lines and take water with you, there is always the danger of pipe freeze. These units are not constructed to withstand long periods of freezing temperatures unless you undertake some serious modifications - mostly suited for hookups - not boon docking.
You could improve things by adding another battery or going to two 6 volts but I really don't think you will gain all that much.
In the long run, you might be better off in a motel if you are left to boon docking with your RV in the middle of winter in the NE USA.
2008 Cougar 5th Wheel 27RKS
2005 2500 GMC Duramax