I am going to install a Bakflip MX4 Tonneau cover on my '05 2500. I am not seeing the drain holes they are talking about me using. All I see are the slits at the front of the bed. I do have a LineX spray in liner that was put in when I bought the truck in '04. Does anyone know where these other holes are? Should I just drill out the slits and use them? I have looked, but not found anything specific to this. Thanks for any help.