Leon

they should be, they're put there to drain out spills.

here's a video of someone pulling a trunk drain plug out of a car:

https://youtu.be/cTI4DTOAePc?t=80

not a volkswagen but it's a very common feature for cars to have

you can pull out one of those round black plugs to drain the water then towel dry or leave it in sunlight for a little while