Thanks everyone for the ideas.
We would plan to move to the northern part of AZ during the summer. We did spend one summer May to Sept through the monsoons and heat in a nice, new Fleetwood pop-up in 1996 in a RV park just north of Tucson, we were a lot younger though. It was the best summer we ever had! Right now, we're doing winter in KS in an RV, and I would trade it for another summer in Tucson right now!
Our concern is the waiting list for services and nothing beyond that with our son. After looking at programs in Kansas, we will most likely have him with us for some time, so it would allow us to change domiciles or set up and live as permanent residents before it might be an issue.
Our older son is career military so he doesn't stay put long in one place although he is looking at retirement in the next 3 or 4 years. If he were settled, we would choose an area closer to him and his family, but the intention is that our son would be in residential although my daughter-in-law actually is a nurse working in adult day care at this time.
They now allow people like my son to have a special account "Able Account" where money can be saved for future needs without penalty to other services like Medicaid.
We don't need an attorney to choose a domicile because of our son. Our son has been an adult for some time now and we are well versed on Medicaid services when it comes to the different states and keep up with changes. Many parent groups are starting to take action and Medicaid is listening and taking actions.