Generally you would have to get all the moisture out of it first before coating it. If there's moisture trapped inside the whole thing will slowly rot.

Just a wild guess on my part but might this item be more suitable to being dipped in a well thinned lacquer, shellac, or possibly varnish than being sprayed? It would probably have to be dipped more than once and agitated just enough to remove air bubbles. Again, it's just a wild and uneducated guess but if it was mine and I decided that I just HAD to add some type of "fixer", dipping is what I'd try.

btw, a very nice keepsake although I'm somewhat surprised that you made it past Customs with foreign plant materials that you probably didn't declare. Not a knock on you, just an observation.