Mostly you will need time! And reservations! Campgrounds in and near almost all the National Parks get full months ahead of time. Figure mid-May to mid-October as the window you have for travel, as many places get very cold/snowy before and after. And the higher/northern places are more like mid-June to Mid-Sept. And then there is the desert heat to consider in the southern areas.
From Tampa to Rocky Mtn. Park (Denver), for example, will take you 5-6 days one way. And then the trip really starts. Figure a minimum of 3-4 days at each Park (that pads in a little down time for laundry, etc.). Of course, you can always add time, and some (Yellowstone area) will demand several more days.
From what you say, you'd be looking at several months! Seriously. We just completed a whirlwind trip from Minn to Colorado to Utah and back, and that took a solid month. A grand adventure, but we should have added at least 2 weeks on to it, just for all the places we stopped at, let alone anything additional.
So start plotting routes, identifying the most important places to go, and making reservations.
