How do I find my cabin gain peak ?

[Fish Chris]

Or, would this be the same thing as "the resonant frequency" of my cabin ? I mean, I guess I could just ask "What is the peak cabin gain in my 2008 F150 Supercab"..... But I'm guessing, especially the fact that it is a Supercab, and NOT a Supercrew, that I'm going to pretty much have to figure it out on my own.

I'm just thinking that when designing a SQL system, knowing where your cabin peaks at, would be very helpful. I'm even thinking about building a 4th or 6th order enclosure.... but I'd want  to avoid creating a peak, where one already exists naturally because of cabin gain..... maybe even shooting for a peak on both sides of that, with a dip right where the cabin gain peak exists. Does this sound logical / doable ???