This will be edited later on once I finish compiling all the different sources and information.
This guy fit a 10″ Xtec sub in an Elise aimed downwards instead of straight or angled up.
one 10W1v2-4 subwoofer in a sealed enclosure. 300 watt power handling. Wired for 4 ohm mono load. This guy has a post of how he did it as well as amping the current 4-speakers
uses an 8″ JL audio sub and is hand-laid fiberglass painted to match your car. Enclosure alone is $500 I believe. (Their site)
This is really freakin cool! Great idea and use of existing pieces in the Lotus
Allows you to install 5-1/4″ speakers all around