I don't know about SNAP, but have worked with plenty of people on Medicaid. As far as being out of state, theoretically you're supposed to notify your Medicaid provider when you're gone for 30 days or more at a time. Notice that I said "theoretically ". But many Medicare/ Medicaid plans now have free virtual visits via your cellphone or computer. You can be in Timbuktu and get virtual medical care now. As far as prescriptions, if you're on Medicare/ Medicaid, if you have access to mail order, you're good. Otherwise you have to get your prescriptions in the state where your insurance plan is based. But that doesnt keep you from having a friend or relative picking up your prescriptions and then mailing them to you, wherever that is.
Where there's a will, there's a way. Some people say that I'm advocating breaking the law, but it's your conscience. Our society wants us to be anchored down into sticks & bricks, but many vandwellers can't afford even that, so if you're poor and stuck living in an RV or other vehicle, you'll be punished for not living in a tent on the streets. We all pick and choose what laws we keep (how many people never go over the speed limit or other "optional " laws?)
Happy travels,
Ted