The problem with powder coat is that it covers the steel, but doesn't bond to it like liquid paint. Once an edge is opened due to grinding or welding, you cannot reseal it and as moisture gets behind it, it will continue to peel due to corrosion.
Also, every edge must be rounded to reduce the surface tension in the finished product or the plastic will thin out too much and fail at the edges.
You'd be better off blasting to a near-white profile, then prime with a bonding epoxy primer, then install and continue welding, grind those areas clean, then reprime with the same epoxy, then topcoat all with a good top coat epoxy.
Powder coat is great for lawn furniture, but not for automotive or industrial applications.
