Depending on the exact specs of your F-150, a 5er may be pushing your limits. You'll need about 1000# wiggle room in your RV math. Agree that about a 28' is a good size. We have a 26'04" and it's great to tow and you can fit it into most any site anywhere. Remember that going too large, can limit your choices.
Interesting choice of locations/seasons....you must LOVE snow and cold to think about CO in the winter. Consider checking various areas you're thinking about to see if they're open during the winter.
Sounds like an adventure....just a man and his trusty dog. BTW, remember to get all your dogs vaccs before you head out and possibly your vet will have some references in the areas you're interested in for that just in case time. And take plenty of HW prev with you as some vets will not allow you to purchase OTC without a new HW check.
Keep us up to date on this, sounds like a great experience.
