Took two tries, but a Red Mage can do this even without /NIN.
Found it important to make use of both Aquaveil and Blink.
Opted for Bio II over Dia II for survivability.
I'm convinced that the dex loss from Rasp helped me dodge blows at key moments to keep Stoneskin and Phalanx up.
Take heart young adventurers, you too can cast lots of DoT spells, hide behind Ice Spikes and still come out victorious.