First step is flattening thwe box between book under weight (for exsample sit on the book).
Then put the box on the scanner straight, DONOPT CLOSE THE SCANNER LID IT CAN STAY OPEN, put hard cover book on the box (bigger than the box but smaller than the scanner bed so it's not resting on the edges) add some weight.
Take a preview scan, if straight ->crop, put moire removal on and scan.