Well I was gonna wait and see what showed up on this post before I went to sanding but I ant a waiting man haha. But I will share what I found for another I sanded the thickness down at the top of the sound board or wall of the box but did not sand all the way to the bottom kind of angled thinning where the lid strikes the box walls and rounding them good on top and not sanding so much even of the whole wall, might be right might be wrong but it worked pretty good!