Hello, this thread will be about how I and my friend prepared for the Terramorphous fight even at sub 50 (around level 40 plus). I just recently defeated it at around level 40 with my level 50 friend, but before that, we had some preparation in hand.
The key to this fight is to farm the 'The Bee' orange legendary shield from a Hunter mini-boss, "Hunter Helquist" from Arid Nexus - Boneyard. You have to complete a quest about disabling his radio station first before you can spawn him over and over again to farm this shield. Below is the video showing his location:
Equip the Vault Hunter relic to improve your chances of him dropping this rare loot. Farm as many 'Bees' as you need for your party size. Next, you have to get a decent shotgun around level 40+ with at least 4k damage X 15 (or more pellets). The reason for this is being that:
With the Bee equipped, it amplifies your damage as much as 30k damage or more for your next hit when your shield is at full capacity. A 4k-5k damage shotgun with 15 or more pellets is capable of dealing 35k damage or more for each pellet, and you can even multiply this enormous damage output with the final Double-Up upgrade for the Commando turret, or Assassin's Deception mode, the former dealing the Slag effect to Terramorphous and the latter dealing more bonus damage the longer you wait in Deception mode before ending it.
As you can guess, I was a Level 40+ assassin and my friend, a Level 50 commando. In short, the battle was short and quick. There were a few deaths to be sure, but as long as one remained in the battle and made use of Second Winds with Terra's tentacles, and the other comes back as fast as possible through the shortcut lift that brings you directly back up from the respawn point, Terramorphous will never have the chance to regain his HP.
Good luck! =3