Perhaps logging on to one ship on a certain account could disable deletion for all its ships.
It would make more sense to me as it means the person still uses that account.
And avoiding that for active players/accounts would be recommended.
A way to prevent too many ships or accounts being created could be being able to unlock them ingame.
So that on one character you'd be able to (dock and) switch to a new ship you've already unlocked.
That way you wouldn't need to create an extra account or character for another ship.
You can still just use one ship on a character for RP purposes f.e. and on the other hand,
would be able to (dock and) switch to something more fitting a certain fight or situation etc.
The server could save the stuff you've mounted and cargo you had onboard & load it when you switch to that ship again.