We full-timed for 16 years and traveled constantly. We made very few reservations with our 40' motorhome during that time even for some of the major national parks such as Yellowstone, Grand Teton, Glacier, Zion, etc.
We also spent the whole summer on a trip to Alaska and only made two reservations - for the July 4 weekend and for 5 nights in Denali Nat'l Park's Teklanika campground which is the farthest one you can drive. We only made those 3 weeks prior when we could better judge when we'd be there. As it turned out we were a little early for Denali so on a whim we boondocked at a lovely spot nearby, drove into the park early morning when folks were leaving and easily secured an additional 5 nights in Denali's Riley Creek campground.
For typical holiday weekends we choose places away from any kind of water - pools, lakes, rivers. We have a nice quiet weekend that way.
Public parks are always our first choice - national, state, Corp, national forests, county and city parks. We also love to find great boondocking spots on rivers or lakes and have them all to ourselves.
That's our kind of camping. We don't need or want the 'best' parks out there. We don't want resorts with packed in sites and gobs of people.
Now, if you need full hookups in popular areas you might have problems. If you can be flexible, it's very doable.
An exception....since you're planning around Rocky Mtn. NP and I assume Estes Park, you'll probably need reservations because it's so close to major cities with large populations. We volunteered at that park and there are some awesome dry camping spots but that's probably not the kind of place you're thinking of staying.
I, too, would recommend that you let hubby have the kind of vacation he wants this time. Don't get all stressed out about it. Try winging it and see what happens. Let him do some input, too. Keep in mind that if your focus is to see Rocky Mtn. Nat'l Park, does it really matter if you don't stay in the best campground? How much time will you really spend there? Good luck!