I failed something awful at this over the weekend; I think I started too close. Is there a specific strategy? After I ate two battering rams and was taking ~79k hits, I went down in no time at all. Got the boss to maybe 50% health.
I managed to drop him in a Demolisher with full pyrite. Just constantly pelt him with pyrite and he should die real quick.
Yeah, I read up on it a bit more after. Seems like you can do it just like you said on 10-Man, or if you switch between 3 different ones (as the Pyrite empties out) on 25-man. The 3-vehicle switch also seems to work for 10-man hardmode. Might try that this week