Just installed a backflip tonneau cover on my new ram.
This cover has water drain lines that fit through holes in the bed.
I didn't like the idea of draining water onto the frame under the bed, so I extended the drain lines to exit underneath the truck.
Heater hose would not fit through the holes in the bed, so I used tygon with the covers lines to fit through. I used heater hose on the bottom so it's not as noticeable.