If you're going to consider adding in RMNP, you will absolutely need reservations if you want to stay inside the park, unless you stay on the west side at Timber Creek, which is all first come/first served. I've already got my first reservations for within the May window, and my first choices were already booked; I even got up early on the "window day" to book and still didn't have any luck and had to go with other choices. Between Moraine Park and Glacier Basin, you may have better luck in Glacier Basin. Watch the window, sites do go quickly.
