So i threw my little jbl boombox into various places in my car and took measurements. I used the smae level for each measurement except for in the trunk, I turned it up for that one. I was looking to find a spot to help me fill the gap my subs have in the 80hz range due to their position in the trunk. My little boombox doesnt play below 60hz but thats ok, I have no issues with my sub output below that anyways. Looks like the passenger footwell area is the winner in my car for that upper sub bass region. Looks like the cabin gain is fairly flat around 80Hz and seems to extend down a little further than the other positions. So I think I will fabricate a little flat box to put there with one of my shallow 8" poineer subs, or maybe use 2 if I can get the air space. I think it will sound much batter than using all that gain from my subs in that region. I'm avoiding messing my doors to try and get those frequencies from my door speakers.