I just repaired a couple of small cracks on my RS PVC armor using JB Weld Marine Epoxy.
https://www.amazon.com/J-B-Weld-50172-MarineWeld-Adhesive/dp/B00R2CDVIW/ref=sr_1_9?keywords=jb+weld+marine+epoxy+resin&qid=1639967273&sr=8-9
My cracks were in curves like yours, and in an area that is too tight to squeeze a piece of PVC into as a backing. I built up some of the epoxy on the back of the crack and it seems to have solidified well. Time will tell if the repair will last, but I'm hopeful.