Any reason rear leaf springs cannot be powder coated?

I have a used set of heavy duty rear springs from a 340 A body to replace the wimpy slant six springs in my 63 Valiant. I have taken them apart, and have a rebuild kit for them which includes all the straps, insulators and interliners.

I have a vague memory that powder coating leaf springs is not a good idea. Is that so?

Alternatively, I can paint them with black single stage urethane, which would be very durable, just more trouble (for me) than handing them to a powder coater.

Thoughts?