100 W can be fine, but requires that you make a concerted effort to reduce energy usage.
Do you have LED lighting? That can reduce energy used for lighting by 2/3, and is the largest drain for many. Cheap fans can draw more power than you think. Use a TV much? Is it DC, or AC with an inverter? Turn off the antenna amp when not used. List and add up what you do use - when off-grid, you need to know what draws what, and consciously limit your use (family needs to turn stuff off when not needed, all the time).
And, a single group 27 battery isn't much, especially for what a 30 footer could be expected to use. If you're running out with lots of sunshine, what are you going to do when it's cloudy?