Wayne Parham Messages: 18789 Registered: January 2001
Illuminati (33rd Degree)
Directional speakers will help a lot, as will multiple subs to help smooth room modes. Then again, garages are often pretty lively and they usually aren't built with any attention paid to soundproofing. Stuff tends to vibrate.
Myself, I might be tempted to hang a few thick carpets or put up some egg crates to help deaden the room. Find any thing that vibrates and tack it down in some way.
You said you aren't planning to stay, so I'm not sure it makes sense to invest in any wedges or panel traps at this point. You would generally make them to fit along the walls, and where you're going might have different size rooms. Still, here is some useful information, in case you decide to go that route: