depending on the cars door panels, it may be much cheaper and easier than you think to do custom door panels. In my car I’m able to cut off the bottom part of the panel, use mdf cut to size, then build off of that instead of doing an entire custom panel. If you are good with working with your hands you would be amazed how easy it is. The hardest IMO is if you are trying to achieve a finish perfect enough to paint. Me I always take the easy way out and just carpet it lol. With .5 cubic feet available, most drivers in the 6.5”-7” size only need just .2 sealed to perform. IMO you have the perfect volume for a dual setup. Mine are currently IB and the drivers really do have a low qts but still have managed to get them to perform well infinite baffle. I know once in an enclosure they will definitely wake up, especially two per side. Let a little time pass and just start buying the material and when questioned, just say listen, I didn’t want this! I don’t want to even do this! I actually hate this! Problem is I need this and had no choice lmao! Works for me most of the time lol.