State park campgrounds in Colorado fill quickly on September weekends if the weather is still nice. And Forest Service campgrounds in Colorado start closing by the middle of September (they are all in the mountains). But, since Labor Day is September 1 this year, you should have more time to camp here before that happens.
Do you have any ideas on the route you might like to take? Interstates only, US highways, gravel roads? Also, can you do without electricity for a few days? Knowing that would make it easier to suggest some of the most scenic campgrounds in Colorado.