Madrone moves a lot while drying.
Best to cut slightly oversized and set it aside to dry.
Make sure it is under 10% moisture content before you use it.
If you use it before it is dry it is likely to warp and/or crack.
But when dry it has very small pores and finishes up nicely.
If you get it stabilized there won't be much of a weight gain.
Used natural (not stabilized) a danish oil finish works out well.