Since you have space for 4 batteries and are going to incur the expense of solar, I recommend getting at least 2x 175 watt panels and a decent multi stage controller.
Although your use of electricity is low now, that could change in the future. My wife now uses a CPAP. This past year I also traveled in the Fall. Next year we are planning a Spring trip. Both Fall and Spring trips will require use of the furnace. The furnace blower chews through a lot of power. In addition for the Fall and Spring trips, the sun is low in the sky and the solar charging is minimal. This past trip I also encountered many cloudy and rainy days. Camping in the woods also kills the solar. The solar panels are cheap.