I, too , would interested in hearing how people deal with this. What you are asking for is "tight" bass.
You have a great sound system for a 20X20 room. Unfortunately, you have it in a car.
There is not enough "room" for high powered low bass in cars. An 80hz acoustic wavelength is about 14 feet. That won't fit in your car. To oversimplify, it "folds"and puts energy in different (higher) frequencies. If your low pass is at 80hz, your subwoofer is generating signal at even lower frequencies which are really slopping up the sound.
Again, I would be interested in how everybody deals with this. You probably notice it'* not as bad with the windows open, because the low frequency signals aren't trapped. Your car acts like a ducted port speaker.
Basically you have tradeoffs with the bass. If you want tighter bass you can't go so low in frequency. But a 125hz signal just isn't big enough to give you a hard punch in the chest. Although if you have an eq, you could add some gain at that frequency.
All i used to tell people was to not get caught up in the numbers game (hz). Only go as low as sounds good to you, regardless of the hz. 125hz is about as low as you can go without resonances stepping in, but what follows below that becomes your personal choice. Trading off depth with resonance.