The last time I was in Yellowstone some campgrounds were hard side only because of bears. You can google the info you need for camping both inside and outside the park. Summer availability becomes very tight and requires reservations. As others mentioned brakes and tires MUST be in good condition. Camping outside the park requires fairly long drives to/from every day and if in summer lots of traffic. Nitwits often clog the roads to get a pic of bears, buffalo and elk if they are seeing such for the first time. I go there in spring and fall when there is little traffic and no crowds at major attractions. If you are adventurous, the back country trails are mostly empty but can be rigorous.
