My experience with contact paper is that it is far from permanent. It was made to line drawers, not to face the elements. It will easily peal from the edges.
Plus it's boring. I plan on replacing mine as soon as I get the chance.
In addition, air bubbles are easy to get. Also, since the stuff has a bit of a grip, any scuffs can actually tear the stuff.
If the stuff was made to go on the OUTSIDE then it might be a better choice. But it was never intented to do so (and with good reason).