New Box Design for trunk in a 1980 pontiac

Hello all, am quite new to this forum and have been around caraudio for a little while but still have a lot to learn especially as I haven't been as passionate as most seem to be here Anyway I have this old car in good shape that I am using to drive to work at the coal mine and have put a stereo into it although most needs to be reinstalled as it is just temporary. I have a 15" RL-p Soundsplinter sub on an SAZ 1500D amp and an alpine HU and some Hertz 165 high power components running on a 400W MA Audio amp I had laying around. The Sub is in a ported enclosure I built a while back for the 08 Charger I had but never put the sub into...... problem is the enclosure is too tall to fit into the trunk of the pontiac so it is sitting in the rear seat right now. I am looking at a new enclosure build here and not sure if I should stick with the same box I have now only a slightly different dimensions so that it fits in this trunk or if I should try some sort of 4th order setup to vent the bass into the cabin. I hate the thought of the bass being trapped in the trunk and want it in my listening area where it should be. Right now its nice having it in the back seat but kind of hard to hide and severely cuts down passenger room Open to suggestions and ideas, have been scrolling through builds and stuff and seeing some nice things one here keep it up guys! Might take a video of the flex happening tomorrow, it is quite loud to me the way it sits right now.