Lee, Locust will make a great bow if properly tillered. I like to let locust, or any bow wood for that matter, cure for a year or more. I have made locust bows with sap wood backs but normally remove the sap wood and chase a ring of heart wood for the back. No problem storing it with the bark on, just check often to make sure that no bugs are boring in there. You were correct on the fretting, that is compression cracks on the belly. I have made a lot of locust bows and have never had a problem with this. If you are careful with the tiller from the start and don't get any hinges you shouldn't have any trouble.
Alan