I've used spar varnish to preserve mammal skulls, (domestic cats, raccoons, opossums, etc) and have had quite good luck w/these. Some of them I've had for more than 20 years. This seems to keep them from falling apart at the sutures (where the bony plates join), however I do suspect that the scutes may separate and pop off in time...if you are serious about preserving the shell I'd suggest contacting one of the curators at the National Museum of Natural History in Washington, D.C. to see how they'd recommend doing this. My suggestion would be several coats of clear epoxy with a "top-coating" hardener..."West System" or "System 3" are both good and should hold everything together. GOOD LUCK