If you can, get enough A/V equipment into the space along with your sub, then place the sub in the listening position and do the sub crawl like I did for my basement TV/theater space (before drywall). I used the Hsu bass test CD for this.
My main listening position will be between 9'-6" and 10'-0" from the front wall and I wound up finding two really good spots where everything below 80 Hz sounded really good while being on the bare concrete floor. It was easy finding the "boomy" spots near the corners, so I moved away from the corner until the "boominess" disappeared but the bass was still strong. Thankfully, I didn't get great response away from the walls. However, I did find a quasi-near-field location (out 5' or so from the front left corner, so fairly near where the sofa will be) and the other sub near the back of the 13' wide by 24' long room (out 5' or so from the back right corner). With those two positions (out from opposite corners), I'll be able to use outlets on either side of the sub and get sub cables that allow for some flexibility in final subwoofer locations once the room has floor coverings and furniture in place.
Remember that the installer works for you and that you have final say in your project. If you can, do the sub crawl--it will be time well spent. I'll follow up with how our room turned out once it is done (late June/early July).
Best of luck!