Subwoofers

So I have a Memphis pr12" in a prefab box chillin in the back trunk space on my driver side. I love it, but I have little trunk space and its killing me. I want to do a fiberglass box on the back left corner but after removing the plastic I found there is little space to work with since the frame comes pretty far in leaving me a small area to work with. Has anybody done any fiberglass boxes on their M2 yet? It seems to be a difficult car to put a sub in with no space sacrifice. Let me know!