Those devices are typically 10-20Ah (this one is 22Ah according to the specs)- that wont get you very far with the stuff skygear is running. a 100w (charging a laptop) item plugged into that would run 1-2 hours if your lucky- and that would be a 100% drain which isnt good to do because its a small AGM battery in there and max DoD should be 80% - 50% giving you the most cycles
they are good for jumpstarting or running very low wattage LED during power outages but that about it.
The nice thing about this is the small footprint it has. And if one battery is not enough it has a removable battery so you can carry a second one. Then the next day while driving just plug in to cig outlet to recharge.
But to do it the solar way you really need a large panel or two and a few deep cycle batteries to do it right but you could easily blow $700-800 bucks on that.
Just google solar power supply for a cabin. Thats basicly what you need. Panel, Batteries, Inverter and an overcharge protector.