I just did this exact same trip camping out of our car. The ONLY thing that would have made it better is if we were on the bikes. Although I do no envy the 8+ hour days droning across the Dakotas/Nebraska...
I suggest you go all the way through Rocky Mountain NP if you are entering on the Estes Park side, the west side has some twisties and tons of NF roads just outside of the NP boundaries.
Also, might be bad timing to ride through the Black Hills NF, Custer SP, and Badlands NP but would definitely be worth checking out if you can stand the pirate rally types out there this time of year!!
HAVE FUN. STAY SAFE!!
Are you camping in Grizzly Bear Country?! The mandatory Bear Boxes really really help but I would still be pretty nervous at some of the campsites we visited this last trip if I did not have a hard sided vehicle. If you are camping I would love to hear your set up for Grizzly Bears...
"...there won't be any money. But when you die, on your death bed, you will receive total consciousness. So I got that going for me... which is nice."