Wheeled vehicles MPA quartered. Tracked vehicles MPA halved. The die roll needed is based on the Morale Rating of the unit, which is predetermined by unit type. Only one attempt per dispersed unit per turn. Units which fail the attempt remain dispersed for the remainder of that turn, at least.
Units being shot at are tough to rally.
Weapon range and Attack Factors are affected by battlefield visibility. These limitations on visibility can be modified if you have ideas or rules about indirect fire, but in that case apply these visibility restrictions to the spotters. In addition, Night visibility reduces all attack factors one half. I hope these work. If they don't, it is completely my fault.