Yeah that would actually create a horrible bandpass box.
The second idea is also stupid because the higher frequencies would be lost in the trunk.
Bandpass isn't complicated if you use software to model the frequency response first.
Sorry how much does it cost to have someone design a box for you?
Better yet, how incompetent do you have to be to mess up a box if you have a forum with people to ask for help along the way?
Because both of those create stupid and uncontrolled bandpass enclosures.
The reason those ports don't work is the same reason using the passthrough doesn't work and the same reason the rear 6x9's doesnt work.
No. What would be worth it would be completely opening up the rear deck, but then again, making a bandpass box would be slightly less permanent.