Any reason rear leaf springs cannot be powder coated?

The heat required for powder coating won’t bother the spring steel at all, it’s no where near hot enough. And yeah, pretty much all the springs for coilovers are powder coated.

Most of the aftermarket torsion bars for these cars are powder coated too. The Firm Feel 1.12” bars on my Challenger are powder coated. 13 years and 70k+ miles and the powder coating still looks great. Might be a little different on a leaf spring since the leaves do slide a bit on each other, but I don’t think it would be a major issue.