Styro or plastic "picnic" cups can be cut to form wheel wells. [img]i/expressions/face-icon-small-wink.gif[/img] Saves a lot of work VS making the well from balsa. The styro and plastic are already fuel resistant too.

I tend to paint the inside of my wheel wells the same color as the aircraft skin in the area of the wheel well. For scale military aircraft... there's a greenish primer color that is often appropriate, or grey or... (any color you think is right for your model is what you should use)