Hi Jerry16,
From my (limited) experience, it is not soundproofing that is going to cut down on the lion's share of your sub's grunt, but more the isolation of vibration through joists and walls. How you construct the room is going to be key to how much the vibrations are kept in check. Direct adjoining walls should be avoided where possible and replaced by floating walls with soundproofing between to keep a lid on the higher frequencies. Using things like rubber spacers between joints can do much to isolate a wall.
It might also be an idea to look at what furnishings you are going to have in the room once completed. If the room is left with the concrete floor and bare walls it could sound full of reverberation like a toilet or bathroom. Soft furnishings such as carpet and rugs can solve this. Misaligned DVDs on a shelf (some pulled out further than other, not just all flush) can also add sound diffusion to the room.
Hope the move and project go smoothly.