There is officially no way that you are "supposed to" do M04, Rain (except that R17, Field Damage, tells you not to do the mission by breaking the model or separating its dual lock.)
As the Field Setup says,
- RAIN CLOUD AND RAIN: Secure with cloud
part facing east. Move and hold yellow bar
north while evenly spreading 9 Rain into the
top. Perfectly even spread is not expected.