It often amazed me that all cars don’t have openings to the trunk. many european cars had seats that folded down to accomplish the same thing, LONG before American manufacturers ever caught on.
I used to pack many a 2x4 into my old 3 series beemers.
The best conversion design was/is the Dodge mini van with the stow and go seats. It can go from all second and third row seats folding into the floor to seating for up to 8. Pretty ingenious design. A piece of crap automobile though.
My former neighbor was a finish carpenter. He used one because with all the seats down you could get full sheets of plywood in the back.