Three months is a lot of time, you should be able to see a lot. I've never taken anything longer than a two week trip in my RV. Here's my limited advice for Yellowstone. I've only been there twice, once was in May and once was in August. In May we saw all kinds of wildlife. There was something to see around almost every corner. In August we saw almost no wildlife other than buffalo, and we didn't see as much of them. I'm speculating that as the weather got warmer the animals did not come out as much during the daylight hours. It also may have had something to do with more people being in the park in August and the animals shying away from the roads during that time of year.