(99 silverado parking break ?

I own a 99 chevy silverado extended cab with the 4 wheel disc brake set up. It has A 5 speed trans with the vortec 4.3 v6 liter in it.My question is how does the parking break setup work. I took the wheel off and all I seen was the disk breaks. Does it use some sort of maybe drum break inside the hub of the disk break wheel.The parking break never has worked but now I have A boat and sometimes when I am launching the boat the truck wants to slip back A little when I leave it in gear.Its kinda scary thats the last thing I want to happen is for my truck to be swollowed up by the ocean.So I need to get the parking break working.Any info would greatly be appreciated....Thanks Joe

Your parking brake shoes are inside your rear disk rotors .