dont give up, if at first you dont succeed rebuild! my first ported box was a mess.. at least it was for my buddys car lol. now im pretty good at this shit lol. try using exposports tuning calculater, it'll give you everything, even accounts for displacements usualy the bass passing throuhg the rear seats or deck isnt a huge problem although it would be louder to port it through. just make sure there is space around the box to get to the inside of the car. also, what did you use to fgure out the tuning of the one you have now? program could be a little off.. or may have build slightly different than specs you punched into the program. either way i wouldnt build sealed, just trial and error, everyone does it. best way to learn imo