Presumably, your two six volt batteries combine to make 12 volts. An inexpensive Harbor Freight kit of four 25 watt panels plus all wiring and a charge controller panel would get you started for about $170.00. This keeps our 150 amp-hour battery plenty charged up for our needs and it helped a lot to swap out all incandescent lamp bulbs to LED bulbs. We simply set our panels on the ground, angled up and move them throughout the day for best power production. And then put them back into a padded box when we break camp.
This will at least get you started and add panels with a higher capacity charge controller if need to capture more power.
Rick
