By heater, I assume you mean a propane furnace. If it's an electric heater, you won't get much use at all out of it from solar power. There are other loads you should be considering: the fridge and lights, at the least.
More generally, the solar would certainly help at least some, even if it doesn't entirely keep up with your electric usage. It's not really possible to estimate anything beyond a very very rough guess without having more concrete data on your electric usage. 200W might produce somewhere around 50 Ah at 12V per day under good typical conditions, or so I've been led to believe...obviously a lot less if you camp in the woods. That's at least within the same ballpark as your usage would seem to be. Heating coffee on the stovetop (or using a well-insulated travel mug so it doesn't need reheating) might be advisable as a simple way to conserve.
