You should put a sealer on the inside and outside of the box, and ONLY on the topside of the paddle. If you decide to stain it you
can.DO NOT apply sealer, stain or a finsh on the underside of the paddle.
You should sand the paddle lightly with like 220 grit sandpaper or finer Lengthwise. When ready then apply box call chalk. ALOT of chalk you buy in the store has wax in it, DON'T use that.
As far,as tuning, make sure you adjust the screw so the center of the paddle is directly on top of the center of the curve on the side of the box.
Lightly sand the top edge or rail of your call. You don't want any stain, sealer on it. I usually sand about 1/8 inch down on both sides of the rail or lip where the paddle rides.
The very top edge of that lip should be lightly sanded to a rounded edge. Be careful not to sand so much that you change the top curve on the top of the box. You should only get noise when moving the paddle in one direction.
This is a start for you. I hope it helps. I am sure there are other people on this forum that can give you better advice and suggestions. I'm only telling you how I do it and I learn more each time I make a call. Hopefully someone else can help you more than me. Good luck. Disney