Underbody plug grommets missing or should the holes be open? VW Cabrio.

I have about 5 holes in the under body open near the front of the car. I have a 1999 VW cabrio GL convertible. What are these holes for? Do I need to plug them up or leave them open? I was thinking its a drain system for the convertible, however, I found the plugs online for sale. I included photos of the holes. There is a circle and an oval on both front left and front right corners. On the front left side, the 30mm circle has a cap but the oval doesn't. The front right is missing both circle and oval. Then a bit closer to the middle, there is a hole on the left and right side about 40mm big. There is almost like a rubber mat covering the hole from the inside. Should i plug these holes with grommets or leave them open? I included pictures.
Comments
You should have a plug for any body opening where water can intrude, such as going through a puddle. Actual "drains" for say the AC, the fresh air vents or a sunroof or convertible top, would be small tube like openings and you wouldn't plug those of course.