the parts that might benefit the most PS doesn't supply., and some of those are custom made, since the only better parts are the custom made pieces why bother with the rest?
if you're building this because you might need it then you should also consider it expendable and not sink a bunch of $ into it.
if i was to do another i might upgrade the door header bars and add A pillars a gusset between those and call it done. the B Bar is adequate as long as the anchor points are solid, being a PA resident 1 might want to ensure that area of the tub is sound. mine looked good from inside but once i tore into it, what was under it was a rotten mess.