i vote trubass that's all i've run for the last couple yrs . went from and orion h2 15 to 3 trubass 8s on the same power and gained 3 dbs . 144db legal on termlab 3 tb 8s on ab 1500w .... with amazingly accurate sq. just bc it ws mentioned i didn't save any space or weight but i did gain some wow factor by having just the 3 8s
You also have a hatch, not a trunk in a convertible. Big difference.
In that trunk, up firing a 15 would be the only way to get it to fit most likely. 3-4 8s would comfortably fit across the front of the trunk and could make much beter use of the space. The 8W7 has no problem getting low sealed. Something like the IXL10 has no problem getting REALLY low in a tiny ported box.