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Is he planning to run electricity back there? If not then the batteries will have to run the lights and cooler whenever the light isn't shining on the panels. I've heard to figure about 8-10 hours of sunlight per/day. On my '93 coach I had 240 watts total, about the same as he's planning and they put out about 15 amps total. So that's about 120-150 amps of charging. More in summer, less in winter. But remember he should only deplete his batteries to 50%. So he should need 300 amp hours of batteries and he will use 50% about 150 amps for 24 hours. That is 6 amps dc right?
So that setup should work but will be minimal. If he has problems then he might want to add another solar panel, and more batteries if he is drawing below 50%
There should be some calculators online.