Why protect just part of it?
I design and build all my own. Everything is designed to carry the extra forces of abuse to the frame, not to critical drivetrain parts, and it strengthens things as well.
Steering box - not just 1/2 of it like aftermarket junk, all of it is protected.
Lower control arms, front and rear.
Engine - from under the front pulley to the crossmember. Full width of the engine, attached to the frame, not the engine mounts or engine itself.
Slider rails extending rearward from the crossmember to protect the driveshaft.
Front and rear diff armor - protects the covers and goes under to protect the U-Joints too.
And of course - side rails.
It's amazing - all that steel and it only adds about 100 lbs.
I'd rather Laugh than Cringe when I hear a "crunch" or "bang" underneath.