Rampart Range Road is extremely busy and it could be a bit difficult finding a spot. And it's a major site for dirt bikes so you can expect a lot of noise from dawn to dusk. As for the road itself, it's dirt but usually in pretty well-maintained condition. Devil's Head Fire Lookout attracts a lot of hikers.
If you want some suggestions about boondocking
around the Denver area, PM me and let me know your requirements. There's places reasonably close.