Edouan,
You are on the right track there. Your trapping should be focusing on frequencies from 28Hz to 240Hz and you should be in pretty good shape. Take note that you do not have modal support for the 1/3 octave bands; 31.5Hz, 40Hz, and 63Hz so good trapping and LF decay response optimizing is very important.
Get a good analysis program to help finalize your setup such as
Room EQ Wizard which is available free.
There is much more info available from
my pubs,
GIK Acoustics and
Real Traps. Good luck!
Cheers,
John