Here's one I built a while back at a shop in VA. Was for a 2014 Escalade.
The guy didn't want any of his cargo space taken up. I went over several ideas with him and this is what we settled on.
It's a ported 2nd row down-firing enclosure for a supercharged DD Audio 3510ESP.
Used this build to train one of the guys in the shop on router basics and stack fab. For a while there stack fab was what the "cool kids" liked to do for the sake of pictures even when it wasn't the best approach to a build. In this instance it was the only way to build this enclosure. Today shops would use a CNC to make something this. I used it as a training tool for a guy that had never worked with a router.
Here's Hector learning some router basics while Belladog supervises.
A few layers of the enclosure cut. Some layers have internal bracing built in. Just routed the bracing into those layers. The math to calculate enclosure volume, port length, and tuning was fun. I was shooting for a Fb of 35Hz. Testing after it was built showed it came out tuned to 35.1Hz. I'll allow it.
Still adding layers.
Another view.
Another view of the inside showing internal bracing routed into the layers.
Closed off the sides. Time to add the extensions to each side that will get proper enclosure volume by adding airspace under the arm rests of the fold and tumble 2nd row seats.
A picture of the enclosure sitting in the vehicle to show the customer how it's built internally and how everything is coming along.
Another view. This time with the seats.
Random shot.
Side extensions going on.