We stayed at Colter Bay and Grant Village Campgrounds in September of 2011 in our 5th W. If you have a hard-sided RV you are good to go. However, you can not leave any food, items with food odors, or coolers outside your RV. If you have a soft-sided RV or tent, you can either keep food in your vehicle's trunk or use the many food lockers supplied around the campground. Both parks are really picky about food safety and the rangers make regular patrols of the campgrounds, especially in Yellowstone. Supposedly they confiscate and then ticket the owner of any food related materials left out unattended as this was the talk going around. For the life of me, I don't recall what we did with our portable grill as it certainly would have lingering food odors...so I'm thinking we put it in the RV's storage bin when we would leave the campsite.
We never did see any bears in the campgrounds. We did see a sow grizzly and 2 cubs in the eastern part of Grand Teton. What a treat!
Didn't see any in Yellowstone.
Have a good time making your plans and a better time going and camping!!