trunk build advice

[spldreams]

hello, I need some advice on the enclosure for my trunk build. I am getting either a dc level 4 15 or an xl 15 powered by a saz1500. my concern is that with the size of the box having it fire towards the rear the sound waves wont have a way to get back into the cabin. I have experimented with a 12 inch type r firing forward and was not happy with the sound or output at all but that may be because it was such a low power application. maybe forward would be decent with 1500 watts, and if i seal the trunk from the cabin. another option would be to have it firing upwards. im not sure the exact dimensions right now but i determined i can fit about 2.75 cubes. after displacements hopefully internal volume is still around 2.5 cubes. any advice or suggestions welcome.