I concur with btggraphix on the wait and see, before adding more. I often use the analogy of a Cafeteria line and picking things to put on your tray. Once you have gone to the end, the cashier then gives you the total. Weighing at the Scale is often the same BIG surprise. Starting out as I did, adding special items take on a whole new world of weight. As an example, my truck/service body weighed in for it’s TARE ticket for registering, came in over 11,000 lbs, heavier than most people’s Truck and Truck Camper combined. Might I suggest you scale your project as soon as you have the opportunity, before you are finished to see what your estimations and true weights really are? It keeps you from being surprised when arriving at the Cashier.
Also, running a heating element device works well when doing it on paper, but reality is this element will impact your SOC (State of Charge) of the battery/s. Thusly, the ultimate health and longevity of your battery bank. Even though a micro wave and other power heavy devices are for brief times, a Space Heater, does not. There are so many variables in maintaining batteries and solar harvesting I would not suggest this as an alternative for heating when off the grid. My battery banks are, 1,460 AmpH (combined) and 1,860 watts of solar (combined) and I would never subject my batteries for more than a few minutes of this steep draw of amps. Theory and reality always have a huge collision, when they meet.
b
