IT focused builds lack duration support so they’re much weaker than other DoT builds. I tried IT and it was frustrating (opposite of what DoT builds should be)
For IT as a secondary focus i recommend Fluff’s Commando - Markovian/Warborn Commando Gladiator Crucible Farmer
the scars of battle+conversion combo: grants you the best resistances you can get in the game against all mobility debuffs, letting you go and fight and retreat at will whatever the amount of slow/freeze/stun etc you may receive
the menhir’s bulwark+sphere of protection: to get a nice total damage absorption
Field command+Inner Focus: to maximize the offensive ability.
But the problem with the BM is the lack of health points in end game, and for this there is the Warder: best default HP pool combo in the game and nice 2H bonuses, but less mobility debuffs resistance, damage absorption etc. Another idea is to go commando for the Temper+Vindictive Flame bonuses+some extra cunning.
The problem with Internal Trauma is that there are too few sources of that damage type, and reflected DoT will deal too much damage to you, cause it’s physical.
My Cadence Witchblade uses Internal Trauma as secondary damage type (along with bleed), it mostly comes from Blitz and Siegebreaker. I doubt it can be used as primary damage type, it’s far easier and better just to use physical damage instead.