Originally I thought I might run a step by step on this painting, but I wasn't that thrilled with the photos I took. Here's a couple shots, though, of the underpainting in progress.
Above, the initial underpainting is about half completed.
I use very thin paint at this stage, just enough to lay in basic values and colors.
Below, the completed underpainting, ready for final paint.
The box has been laid in with a second coat of paint.