P-rod cheek rest

I have seen that some people on here have made cheek rests for their P-rod stocks with a piece of 3/4 in square doweling, some aluminum spacers, and some screws. I am thinking of doing the same thing, but I have a question or two first. What size screws are you guys using? Are you putting inserts in the stock, or do you just drill straight through? Is the stock hollow, and if so, is there a chance of me doing any kind of damage to the stock by drilling?
Thanks in advance,
Chris