my 4 iinch thick bass traps eat up 21" of wall space on either side when placed in corners. I think they'd eat up too much space. A better bass trapping set up would be eight panels of 703 (or Johns manville stuff like I use.... same stuff) placed two panels thick on one of the walls with an airspace behind them of two to four inches, mae with scrap wood spacers of soem sort. (Try with two and maybe increase if not enough bass is being eaten by them) THis would eat up six inches of your space, but only six, and would definitely take care of the bass.
You could probably get the same thing done with fewer panels, but make use of airspace behind whatever you put up as that is key to absorbing bass, since the long wave needs to spend as much time in the 703 as possible, and if it has some time before hitting the wall and bouncing back, you'll be able to hit more of the length of the wave.
You could also just thicken up the 703 up on the ceiling, again with airspace behind it, and still trap enough bass to impact that boxy sound. In fact, that's the longest dimension of your room and that may be best at absorbing the longest wavelength of bass (that last part is a guess, but makes intuitive sense to me. I don't know if it's accoustically accurate.
One major problem with your space is that your dimensions are factors of eachother. If your 8' wall makes nodes and peaks at wavelength x, it will also make them at wavelength 2x and 3x and 4x. Your one 4' wall will make the nodes and peaks at 2x and 4x, too-- totally screwing with the sound at those frequencies. And uh oh.... there's another 4' wall distance that's screwing with the same frequencies, doubling the mipact and screwyness of the response of the space! Yeccchh!
The more I think about it, the more I think that a deep layer of 703 up at the top of your booth, wrapped in canvas, and heck, even recovered in the auralex that you pulled off, would really be more convenient, comfortable, and solve a lot of your problem.
