I don't get it. Why do you want dimensions from another box if you are building your own? Unless you are using 6" woofers or something it won't be too big. Back in my car audio days we built the box as large as possible to fit where you want it. You know? Has something changed? Or are you wanting to build it just like the Subthump one for some reason?
To be honest, it is because I have a baby seat installed right now, and don't want to take the effort of pulling that out, removing the plastic cover and metal bar under the seat to measure out what might be the right size, then reinstall everything, build the box, uninstall everything, test fit, see I made a simple mistake, reinstall everything, rebuild the box, etc. you see where I am going with this...
I figured it would be easy enough for someone to grab a few quick dimensions from the box we already know fits.
What I want to build will be a single woofer with amp space, but also maintain some storage space that I can access without having to flip up the seats (again, because of the baby seats that will be installed).
Back in my car audio days, I drove cars with trunks or SUVs/hatchbacks with cargo areas, so you could build a simple square box by just taking 3 measurements (L x W x H). The most complicated part I needed in those cars was a hinged panel that covered a storage area and provided protection for the speakers from the other items that might be rolling around in the trunk. That panel was contour conforming to the trunk wall and hinges.
Obviously with these trucks, really the only place to throw a sub and amp is under the rear seat, and since both baby seats will prevent me from pretty much ever using that space, I might as well use it for a sub box.