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Solar power - definately the way to go, as I've got one maybe 12" by 36" in my mighty diesel van to keep the batteries fully charged, and that panal (plus regulator) works like a champ !!
Maybe it's 10" x 28" but it's nothing major, and it will power reasonably sized 12 volt devices too :)
 
I've found the set up I have is great for everyday use. I guess it all depends on what you plan on running and wattage /hours. my batteries are never low, in the past I have woke up in the middle of the night to the low power alarm going off.