I'm not sure what sort of projects that you have in mind with the rawhide. This would determine what your options would be for the finish...if at all.
I have manufactured dozens and dozens of primitive bows backed with rawhide. Naturally, if these bows were going to be used during damp or wet conditions, a good sealer would need to be applied. I (and others) have used my rawhide backed bows in the Alaskan and Canadian bush where it rained and poured for the entire trip and never had any moisture issues. Moisture can cause rawhide to separate from the back of a bow much like it does with a sinew backing.
I use a combination of things to seal my rawhide backed bows. My own personal bows are sealed with Tru-Oil (several coats) which is super easy to reapply if it gets chipped or scratched. I maintain a paste wax finish over the Tru-Oil to insure a complete seal. I have also used a combination of spar varnish, linseed oil, and mineral spirits, or a combination of cedar oil, linseed oil, tung oil, and French polish (French polish is a combination of shellac and linseed oil), all with good success. Too, I have used simply polyurethane sprayed over the rawhide bow with complete satisfaction. With all of my rawhide/bow finishes, I still maintain a good layer of wood floor paste wax just to make sure everything is completely sealed...especially when hunting deep in the bush when making archery tackle repairs is out of the question.
I also use a rawhide interior or liner for many of my custom-made sheaths or boxes for historical re-enactors. I use a special homemade resin/glue to keep these as water-resistant as possible (dangerous and a pain in the butt to make). If the rawhide is going to be glued to something (like wood), I use either a flexible wood glue or hide glue to made the bond. Do not use epoxy. The rawhide will be rock-hard and should be sanded and finished like the wood. You can see through the rawhide backing on my bows and the rawhide is as smooth as glass when finished.
-Danny
