This is what I have.
Sunforce Solar 5W Battery Charger
I wired into the Battery line in the electrical box under the pin box and leave it laying out in the sun to keep the batteries topped off. I do go check the batteries ever so often to make sure they've still got water in them. This one doesn't have a controller - It's not big enough to need one. If you go larger, a controller will be needed to regulate the input voltage. Many panels can be daisy chained to get a larger input levels. I've heard that some people have done this to keep their batteries charged and run 'some' AC things through a converter while dry camping.