Oil Pan : bare steel inside ? Options

[jsteele22]

So I'm getting close to hacking up the oil pan on my Subaru engine to give more ground clearance. The stock pan was painted/coated with a great, durable, smooth finish. I've alread got that blasted off. I have no idea how they got the insides, including the oil pickup tube, underside of splash tray, etc. painted unless it was dunked.

I'm going to cut the bottom and braze on a shorter, wider pan (with baffles) which I plan to make out of mild steel. The outside I plan to powdercoat. But I don't see any way to get the insides covered. Is it okay to leave this surface untreated ? On the one hand, it's gonna be spalshed with oil, which protects against rust. But OTOH, I know motor oil can get moisture in it if the car is driven on short trips (which I do) and left to sit for long stretches (which I do), and also that blowby can deposit some real corrosive stuff in the oil. And the mild steel rusts in the blink of an eye. I filled a small mock-up tank that I built with water to look for leaks. Within hours there was brown rust forming.

Any sage advice from the old-timers ?