As far as I know Grumman always painted the bottom side including the wells and the bays in the same color as the underside of the wing.
I was just going by what I've seen here. I've never done scale, I have a ModelTech P-47 but it's stock. After going through this thread I can't resist giving it a try. I'm pretty slow though. Even with nothing else to do it will probably take me all winter.
Yeah, I love this thread too.