I don’t think you’ll run into any probems really. If you wnat to go to Winding River, you may want to call them to see if you need reservations. I think you might need them in July.
A nice newer park in the area is Hermit Park. It was a private area but was purchased by Larimer County. I haven’t been since Larimer County took it over, but spent a lot of time there previously. It’s a very nice area and had a primitive camp ground (with bath house) and primitive cabins - along with some corrals. That might be something to do if you and your horses have a free day. You can even ride from there to Lyons - all very pretty.
If you want me to pick up any information at Rocky Mountain National Park, such as a map and their pamphlets about horses in RMNP, let me know. I can easily pick some up and put them in the mail.
I did ask around about other places fitting your description and haven’t heard back yet. Most of the paces I think about are primitive camping. I do have a file of trail, horse camping information and will go thorugh it. If I hear back or find anything, I’ll add it to this thread.
Looking at information on the Continental Divide Trail (goes through RMNP) and Colorado Trail (SW of Denver, but intersects CDT), might give you some more ideas.
I’m with you, I’d head for the high country! The plains and grasslands are beautiful, of course, but the mountains…oh, the mountains!