I am on medicare with uhc as a backup. I am full time rving so I have a mailing address. UHC says it is not in the area where I signed up so they will drop me. What can I do to make them understand I am traveling and this is only a mailing address.
As others have mentioned, there is more than one issue at stake here. Do you have a permanent address which is used on your driver's license, vehicle registration, and other insurance? All of those require a permanent address and under the law must be done at your physical home. If you moved those to the place where you receive your mail, which I am assuming is a different state than where you now get your Medicare supplemental insurance, then legally you have moved your residence.
At present, insurance companies are licensed in the state where they operate and are not allowed to sell coverages across state lines. In addition, there are differing degrees of risk from one local to another and so premiums vary by location. In the future it is said that the new health care laws will be changing that, but for now it is the law for licensing and each state controls the insurance sales inside of it's borders. In addition, the insurance companies are still allowed to make the rules about who they will write coverage for and so unless you have some permanent address to give the company, you will probably have to move your coverage. It really isn't a case of them understanding it is a case of their rules and licensing. They are probably looking for some form of proof that you really do live in their prescribed area. If by UHC you mean United Health Care, you can get it in most, if not all states but you will need to get it via the state of residence and the premium may be different.
Domicile is actually a legal term and is not defined in the law but is determined by a court if a suit involving the issue should arise. It is determine by the combination of all business and living activities that a person does. In the case of fulltimers it can be unclear, but for most people it is pretty simple because we do most everything in one location, where our stick homes are. I suggest that you might find it useful to read this article from Escapee's Magazine about domiciles.