why don't you do something like this, with a 10 or a 12and save your space.
http://www.subaruforester.org/vbulletin/f77/duffman-spare-tire-well-box-56919/?highlight=yerrow
http://www.subaruforester.org/vbulletin/f77/duffman-spare-tire-well-box-56919/?highlight=yerrow