Before Installing Tonneua Cover Drain Tubes, I'm Asking For Advice

[Goose55]

I need to install two rain water drain tubes on each end of the bottom of this retractable tonneau cover canister, and run them out through the bulkhead of the 8 foot bed of my 2019 3500. I see here at the very bottom next to the rubber bed mat, an oval shaped--what is it, a removable plug? It's maybe 2 x 1-1/2 inches. There's also another one on the passengers side. The drain tube is just shy of 3/4 inches wide. My gut tells me that--if that oval is a removable plug--running the drain tubes through that low would create issues when I run stuff that far back. Instinct is telling me to instead drill a hole much higher--maybe 2 or 3 inches below the canister. What do some of you think?

Thank you!