Ducati Monster 1200 Owner's Manual page 202

Make sure clips (6) are in place.
Position the two covers (3) under the seat, by
correctly inserting the tabs (L) on cover (3) into the
slots on underseat cover.
Tighten the four retaining screws (2).
200
6
L
2
3
6
Fig 128
2
3
Fig 129