[xb-60]

Powder coating is very popular, but more expensive than wet spray (particularly for large items). If it chips, the damaged area on a powder coated surface is more difficult to repair effectively. Powder coating is slightly more porous than a wet spray (but not much in it). I would go with a wet spray.
I don't know anything about POR15 other than what I've read. It sounds like good stuff.
Cheers,
Glen