Preserving a turtle shell

Found a turtle shell in a chunk of ice with no turtle in it. Smells a little strong but not overpowering. Once it thaws, what is the best way to preserve it? Searching the web did not yield real specifics. So far have found suggestion to let bugs clean it and leave it in the sun to dry. Or, put Borax in it then paint it with Polyurethane/soak it in unknown amount of Borax, salt, and water-then in vinegar and water. Anyone have any experience and more detailed advice?

I have a turtle shell I found wandering around the woods of western Tennessee about 30 years ago now. I never did a thing to it other than wash it down to get all the smelly bits out then let it dry in the sun. It still had the "skin" on it when I found it, but that eventually dried and flaked off in the shaped of the scales themselves.
Letting ants at if until they decide nothing is left for them, then washing and sun drying probably isn't a bad idea. Can't hurt to try, I'd just be sure and protect from something deciding to cart it off.