You can also use klass kote epoxy for a top coat and it is impervious to nitro at least to 70%. It goes over most everything except urethanes, but nothing else will do that either.
Reasonably priced and you can have just about any color you want with some mixing. They also have military colors.
If you have access to a decent spray booth then auto clear coat is the way to go. However don't do this yourself without full knowledge of it's potential lethal consequences if you don't follow all safety rules.
Dennis