If you're retired and are on no timeframe, just go and have a relaxing trip. I can't imagine leaving Florida and having reservations for your whole trip out West. You'll miss seeing many neat things along the way if you're so scheduled. Especially that early in the season, if you stay just outside the national parks the previous night and drive into them early morning, you'll get a site. If you come into them late afternoon, then, no, you probably won't get a site. The key is getting there early when folks are leaving. Even in the campgrounds that accept reservations, there are always cancellations if you're there in person. With our 40' motorhome we always find sites in the national parks of the West. Have a good trip!