RE: Propane in national parks - if they have gas stations they sometimes sell propane, too, but don't count on it and it will be very expensive. Try to fill before entering the park or carry your tank in the rear of your truck as you're siteseeing and perhaps scoot outside the park to fill.
89 north to Page. It will be no biggy for you but be aware that the highway just beyond 89A intersection is closed and you will encounter a very easy detour on a good paved road which runs roughly parellel to 89. It's easy.
Entering Zion - since your RV combo is short you will have no problem entering from the east and going through the tunnels. That's how you plan to exit anyway. If you're taking 89 out of Page this will be the shortest route. The other route is very good but if you're staying in Zion it will be longer for you.
Hwy 550 from Silverton to Ouray will not be an issue for you. Gorgeous drive!
It would be a beautiful drive after Ridgeway if you took Hwy 50 from Montrose to Salida/Buena Vista/Leadville to I-70 and pick up 40 to Granby and enter Rocky Mountain from the west over Trail Ridge Rd. That would save you from driving Trail Ridge again once parked in Estes or wherever you're staying, and you 'must' drive it.
Then head south on I-25 to Colorado Springs and back home. By that time you'll know how much time you'll have for the Springs. You might run out of time by then!
