You will have very little problem towing a 35-37 foot trailer on major highways in Colorado. My brother-in-law does it all the time with his 36-foot Outback TT. Only if you try to tow it places like over the Million Dollar Highway from Ouray to Silverton, Trail Ridge Road in RMNP, or Rimrock Drive in Colorado National Monument might you have a problem.
However, you will not fit into most Forest Service campgrounds in Colorado, which generally have few, if any, long campsites or pull-thrus. National park and monument campgrounds in Colorado may have some long campsites, but they will require advance reservations during the peak summer season. Most Colorado state parks have long pull-thru and back-in sites, but, again, they are limited in number at some parks. We have a short 5th wheel, which we special-ordered so that we would be able to fit in all those tight campgrounds in the Rockies.