Re: Domicile or Residence...
When we lived in a foreign country, we kept the state where we had lived in previously. It is a state without state income tax. It was a slightly different situation, but I just used my parents address if for whatever reason I NEEDED to put down a physical address.
We now live on a boat in the same state, and the few times that someone has NEEDED a physical address, we generally give the marina address, I will confess to not changing my drivers license yet, so I am not sure if it will be PO Box or Marina on it . . .