Although I'm sure it can't hurt, I've never felt the need to add anything to preserve bone handles (jigged or not). I've collected many bone-scaled knives over the last 20+ years, and most of that time has been spent in the relatively hot/dry southwest. No issues with shrinking or drying out. Bone is generally very stable and durable, aside from the occasional cracks that result from stresses around pins, or from dropping/impacts. The stress issues around the pins are usually due more to defects in the bone or the construction (such as cracks resulting from drilling the scales for the pins), from early on. Otherwise, it holds up very well on it's own.