Bill,
I've camped in the Yellowstone area for years and have never had any problems
with bears. We always keep our food in our van.  We keep the camp clean and
the stored food out of sight.
I've heard that Yosemite is another story.  Don't know much about that except
that I've been advised not to leave any food in a vehicle there.
Good Luck, Have fun!
Jim Woods, "91 Syncro Westy, Jackson Wyoming