It's got foam blocks cemented to the underside of the seat or flopping around loose, depending on your boat. In mine they're about 50/50 still cemented in place or loose.
There are a couple of stringers in the vertical and horizontal surfaces of the seat. This picture from the facebook daysailer group shows it well:

- transom xsxn.jpg (437.13 KiB) Viewed 4223 times
Never done it myself, but that big round stringer sure looks like a nice conduit for a wire...