Residency for Full Time Rver w/own lot?

[2203sp]

My husband and I are retiring from IL and moving to a lot we purchased in Mobile County, AL. We have sold our home and will be "living" in our RV on the lot (there are no restrictions) until we decide to build or buy a house. I am having trouble establishing any residency (for insurance, drivers license & registration, mail, state taxes, voter registration) because the county refuses to issue us a physical mailing address until we purchase a permit to build (I'm not even sure this is a buildable lot!?). I have talked to everyone in the dept. and I still get the same answers. We have the deed and title with the legal address but until there is a livable permanent structure, they will not issue a street address. Our only option is a P.O. Box but it is not accepted for all the aforementioned government documents. Legally we are required to register our vehicles and get a new license within 30 days of moving, I am trying to abide by the laws but don't know how? We would no longer be IL residents and would be living in AL so this would be our legal residence for tax pursposes, etc. Would an Affidavit of Domicile do any good? What do I use for an address on all these things? Please help, I have no where else to turn!