Will a 100 watt solar panel be enough

The only way you are going to know is by doing an assessment of your actual use. A 100 watt panel will produce up to 30 amp hours per day under ideal conditions, less if you don't follow the sun, and on cloudy days. Many owners of small fiberglass trailers have no problem using a single 100 watt portable panel, others require far more.

If you winter camp, and run the furnace, it will be difficult to keep the battery up.