Coaming pad, with some glass behind it. If memory serves, the opening is larger than what is pictured with some of the opening extending behind the pad.
Best way, remove the panel, remove the around the work area. If the foam is think, you are best to recess the speaker into the foam, rather then compress the foam and vinyl with the speaker mounting screws.
What ever you do, DO NOT cut a round hole out of the vinyl. As you try and mount the speaker, the vinyl will creep out from under the speaker.