I say use a plastic filler with a colour as close as possible to the main colour on the sub.
Since it's only this small line that needs to be covered I say use a small spatula knife and use very little filler at each moment.
Let it dry and then sand with a toothbrush covered with sandpaper..Starting with low numbers and end with high numbers. low E.g 250/300. High E.g 900/1000.
It doesn't look beautiful this line going all the way around the sub. It somehow destroy the look of it. And you want your model look as realistic as possible.
I also recommend you use this tool after sanding
https://www.scalemodellingnow.com/hn...ll-rivet-maker
Markus