Have any of you guys replaced the outer rocker piece by itself or used one of those slip over pieces?

Me myself , no, because it was already done.. (on the outside) but i did the inside.. NEVER use slip over stuff.. it's a bad way of "replacing".. it's covering up a lot of ****.

Always take the rusted parts out and replace them..

Btw... are you making your own chassis ??  I think you are replacing every piece on that car? 😮