Check out Great Planes' Plan Protector. Works great and is clear.
http://www.greatplanes.com/reviews/gpmr6167-rcr.html
I would not bond anything to your door. You're going to want to replace the surface at some point.
ORIGINAL: Mojavegold
Thanks to all of you for the great info!!

I think I will give the homosote some serious consideration. I'm starting a balsa usa 1/4 scale cub build next week, so this info is very handy. Any thoughts on 1/4 inch thick cork tiles bonded to the door surface? My only concern was that they wouldn't all be the same thickness. Also, I was thinking about using wax paper over the plans, like we used to do way back when. Unless there is anything better out there.