|copers are hard plastic cut up to fit over your trucks.
in the old day of pools, grinding was much easier if you had them vrs trying to grind the metal
pvc is a hard plastic pipeing used for pluming usually.
attached is one company version
with pvc you would just cut out enough so they "clip" onto the truck by themselves. cut more out of the middle to accomadate the king pin and not so much around the ends.