That rear stone guard is beyond saving. I was never sure of the purpose of a rear stone guard - on the road, stones hardly ever get kicked up against your trailer from the rear. Apparently TM felt the same way - pictures suggest that they don't include a rear guard any more. So you should probably just remove it and discard it.
The front guard can be saved. Regardless of how you end up doing it, the first step is to drill a "stopper" hole, maybe 1/8" diameter, at the small end of the crack, to prevent it from propagating further. Beyond that, my approach might not have been the best - others will chime in - but when I did it, my first emphasis was on binding the sides of the break tightly together. I crafted a small 1/16" thick aluminum patch that would fit snugly inside the guard, covering the crack. It was maybe an inch wide, and long enough to cover the entire crack. I pulled the edges of the crack together, then drilled 4 holes through the guard-and-patch sandwich, and pop-riveted the sandwich together. Painted the outside ends of the rivets white. Then I globbed on some kind of goop - I don't even remember what - with the idea of further stabilizing the joint.
I thought about including some fiberglass mesh somewhere in the sandwich, but ended up not doing it. I'm not good with fiberglass, but other Forum members are, and you will hear from them. But those first steps are important - drill the stopper hole, and stabilize the joint.
Bill