Kicker Q Class Enclosure Build

[dolbyatmos]

Hey guys, I'm pretty new to the car audio scene and was wondering if I could get some help designing a subwoofer enclosure. I will attach the T/S parameters of my subwoofer. I have a Kicker Q Class 15 inch subwoofer. Currently I have this loaded in a Q-Bomb enclosure thats tuned at 37Hz. The problem I have now is weird, when I open the rear hatch in my Mercedes Benz I get crazy low frequency extension but as soon as I close it the low end goes away. Do you think this is because the subwoofer needs more air volume inside the enclosure or the fact that the enclosure is tuned to 37Hz? I feel like thats high for a 15 inch driver. I will attach the box I have designed, just please don't laugh because it's tuned to 28Hz and simple.