2004 sierra ext cab sub box troubles

i have a 2004 gmc sierra ext cab  , i used to have a 2001 same truck i bought the jlaudio stealth encloser with 1 10

i put it in my new 2004 today and now the seat wont lock in place in the down position its real close but it wont lock anyone know how i could get it to lock or if they changed this box since 01  here is a pic of my box it dosent seem they changed the seat at all but it will not lock in place . any tips will be greatly appreciated.