Cut and bend small mounting 'tabs' that line up with the speaker mounting holes. *

You can see how the speaker will rest on these tabs.

Use Household Goop or other silicone type adhesive to secure the mounting tabs in their bent-down position, and secure the speaker in place.

Here you can see the speaker securely mounted. But we still need to deal with the air space around it!

Use duct tape or masking tape, and carefully block off the air space. Ideally you'd just fill this area with silicone, but the gap is wide enough for the silicone to drip down. The tape will keep it under control.

Everything siliconed in place and ready to be mounted.