RE: Palm Creek.....keep in mind that it's a far distance to do anything in the greater Phoenix area or in Tucson. You'd be putting on a lot of miles and time. There's not much to Casa Grande except shopping and restaurants. Depends on what you like to do. If hiking is one of them then choose one of the other two areas for awesome hikes and most bigger RV parks have a hiking club.
Also, Casa Grande can get dust storms. We've been in two driving on I-10. Scary.
Personally, I'd recommend that you break up your winter stay between the Phoenix area and Tucson. There is just so much to do in both including cultural activities and the spring flower siteseeing opportunities are great.
You might also consider the Maricopa County (Phoenix area) parks. They are top class in sites and scenery. McDowell Mountain and Usery are favorites and are good for big rigs. There's a 2-week limit. You wouldn't have the 'planned activities' that RV parks might have but the surroundings can't be beat and hiking right in the parks.
There's also Lost Dutchman State Park which can't be beat for location, drives, hikes, flowers, campsites with mountain views. There are many wonderful sites for big rigs. We've volunteered there.
Catalina State Park in Tucson is the same - back right up to the mountains. Both are extremely popular as are the Maricopa County parks so make reservations now.
Since you're only planning on a one-month stay, break it up and tour each area for your return trip. You'll find what's best for you.