I don't know if contact paper would be a great idea...it's a real pain in the ass to get off, leaves a lot of residue and because it is pretty flimsy, could possibly warp or bubble up if your case gets really hot.
I would suggest using an art spray, like the kind painters use to protect canvas once they're done. Krylon makes a clear acrylic spray, but if you dont' get even coverage then it might look crappy.
If you can find it, probably a sheet of static-cling plastic would work. And here i don't mean Glad Wrap, but like that rubberized stuff they make removable stickers out of. It's easy to cut, and easy to remove/reposition and it doesn't leave a residue.
Don't ask me where to find any tho