If the vehicle is outside of
If the vehicle is outside of the UK for more than 1 year it is effectively being exported. You would legally need to export it from the UK and import it into another country. Of course this is just paperwork. The vehicle can still travel over borders.
As you say, if you move between other countries frequently then changing the country of registration would be a hassle.
Is there no way of having the vehicle return back to the UK once every year?
Do you intend to return to the UK eventually with the vehicle?