Here's my two bits, coming from a bass player, not a car audio guy.
Those "holes" are ports. There are some cabs (enclosures) that are designed to have ports, and some designed not to. Just adding them probably won't help. Your boxes might not even be designed to spec for the speaker... just boxes.
Bass is about moving air - from what I've read, circular speakers are better at it. That's why people rip on the funky-shaped Xplod subs. 6x9's exist only because of fitment issues in cars. The flat bass might be all they're up for.
is the 800 a RMS or peak? Ohms? These are factors - it might just be underpowered when splitting a 115 watt amp. Try hooking up just one speaker and see if you get better sound.
The other option is to hire me & my G&L/Mesa-Boogie to ride in your trunk...
