Help Me Take Down a Vastness

[Stryke11]

What is the deal with these guys? I'm playing LE Marignon and I knew that Ryleh becomes an unstoppable force in the late game so I was lucky enough to find a land based shambler province near my capitol. I immediately focused all energy into building a full independent sea army. I have since wiped Ryleh down to just their capitol and two land provinces but they keep moving their army of two vastnesses and their ghost king around and nothing I can stand up against them (early game, and Marignon has no access to high level water without empowerment and my pretender is a Baphomet with blood, astral, and fire). I routinely lose 100 guys or more to these three, and maybe if my swarm is lucky I take down about 10-20 hp from them before they rout. The real killer is the blood revenge or whatever that self damager is called. Getting mages into the water is hard. Any ideas?

Also, though you may not be able to recruit PD or build national troops, I see no roleplaying (or game rules) reason why you couldn't build a fortress underwater using an underwater leader which simply allows resource allocation for building more of what is already there (in my case, Triton Troopers, which are very resource intensive).