Trying to figure out if it’s at all possible to fabricate a 7-8 cubic foot enclosure to fit in the trunk. Has it been done ?

 

8 cubic feet is a 2 foot cube. That's a BIG box. You could probably make one fit in a Lexus trunk, as long as you didn't want to put anything else in it. From the size I'm guessing it's ported. You might want to consider a sealed box design. Unless your goal is to set off car alarms in the next block, a GOOD 10" sub will provide all the musical bass you can stand inside the car.

 

What model car?