Other part I forgot to mention is cabin gain, or the frequency your car is going to naturally amplify on its own. This will change your response curve somewhat also, but is not something you can really model as every car is different. It could mean you'll gain back the low-end. Or possibly gain some higher frequency, leveling out the response. Either way you're going to have loud head knocking bass!
When you get tired of just being loud and low as possible, you can always smooth things out a little with the EQ, level the output with the frontstage and make it more acoustical. Or depending on how easily you can get to your adjustments, possibly have two different settings. One for all out and the other for easy listening.