Before buying, check that the roof of your caravan can support the weight of a solar panel as some won't.
Also, a flat panel is less efficient than one that is angled, so it may be worth looking at a portable, folding solar panel.
Solar panels used in this country are not very efficient due to our unreliable sunny weather so make sure you find a panel that will meet your output needs.
I have a 13w folding portable panel that is sufficient to keep my battery topped up over the summer months but I only have 2 small LED lights that run off my 12v battery.
Just some things to consider before you part with your money.