i believe this is it, i think they told me the one they had was 75 watts though
http://www.crutchfield.com/S-0OGzru0CWL6/p_500KTP445/Alpine-KTP-445-Power-Pack.html
even then 45 watts is a bit more than 18
http://www.crutchfield.com/S-0OGzru0CWL6/p_500KTP445/Alpine-KTP-445-Power-Pack.html
even then 45 watts is a bit more than 18