July is a really busy RV time across southern Colorado, and the rest of the state for that matter. I prefer reservations in advance so that I know I will have a site waiting. Many people do not want to be held to a strict schedule. You should at least call ahead as soon as you know where you want to spend the night. Even at that you may not get your first, or even second, choice. I would not recommend starting to look for a place late in the afternoon.
I use rvparkreviews.com to check possible RV parks that I may try. There are other sites to get ratings also.
Don’t know where you are starting from, but Pensacola to Denver is 1,500 miles or 3 long 10-12 hour days on the road. And that just gets you from the tip of FL to the front range of the Rockies. 3 days back leaves you only 8-9 days to cover a lot more miles with little time to spend at each site.