My take on the Umbral [Inaros] idea. Basically, he's completely immortal, cannot be knocked down or knocked back, is immune to status effects, and always has energy coming in for pocket sand. You can use any of his 3 Augment mods (Negation Swarm is for tanking, [Desiccation's Curse] for pocket sand, and [Elemental Sandstorm] for big status effects on everything) but this is my preferred setup.

To fit [Corrosive Projection] in, you need to take away only 1 point from 1 other mod, whichever seems the most worth dropping. In my opinion, [Hunter Adrenaline] would be a fine option for this.

Is it a 100% optimized build? No. But you've already seen this. This is something a little more flexible and fun, and gives you some options in how to play. Add a second Umbral Forma and you can have even more flexibility.