In many states Blue Cross Blue Shield will not write policies unless you have an actual street address (mail service street addresses won't work - they check against a database file to make sure you are not using a commercial address) and you spend at least six months each year in the state you claim as a legal domicile.
If you have a policy provided by an ex-employer as a pension benefit they will write a policy without the requirements above.
In NH we used our daughter's address where we "rented" a room and since we spent May through Oct in NH at that time we met their requirements.
When we moved to SD they refused let us keep our policy so we had to go with another company (Assurant) that did not have the restrictions.
You might want to check and see what BC/BS requires for the state you choose as your legal domicile.