Rocks top pic, wood bottom.
Regarding the hole for the rattle, they make a commercial grade plastic core device made out of brass, I believe. But a buddy of mine uses sections of an old telescoping car antenna. It has several diameters to accommodate different size rattles. Yea, I remember they used to make a fizzing alka seltzer product for tubes!?
We leave the craws in the packaging to maintain shape; but you could put them in a bag with scent if you want. Keep in mind that the movement of the claws is important, and if they are out of shape or twisted incorrectly, they don't quite act the same.
5/16 oz seems to be the best size weight for the craw for most river conditions. It will get down pretty quickly in current and you can reasonably fish it down to 10-12 feet pretty easily. You might need to use a tad heavier equipment than you are currently using. I like a medium or medium heavy fast tip rod, 6-7' long. 12-15 lb test line.