Agree with Bryce as a "do not miss". Take the shuttle in and take the walk along the canyon back down to the next shuttle stop. Ask the ranger in the visitors center - it is a popular option and so worth the time.
Also agree with Springdale or even Hurricane as a better choice. WillowWind RV Park in Hurricane is where we stayed. It is less than 30 minutes from Zion. Be prepared for crushing crowds in Zion even during your timeframe. We just did the September/October Utah trip this last fall. Same with Arches.
Canyon Lands was by far my favorite. Do not miss all of the overlooks at the north end of the park as well as Dead Horse State park. Monument Valley is worth the trip but you don't seem to be going that way.
Weather can be challenging the later you stay. Just pay attention to the long range forecasts. You will not get snowed in or stranded but could put a damper on seeing the sites and being comfortable while doing it.