What is a good and hard clear finish for a soft wood gun stock? The wood is so soft you can dent it with a finger nail very easy. Thanks for any help.

60 year old house with wood ceilings, lap board, but time has caused gaps between the boards. How can I seal between these boards and keep the natural finish? Gaps range between 1/16 and 3/8. Right now my heat is pouring into the attic.