[FG28_Kodiak]

No it works for Groundgroups also.

Ok it not work for trains :/

but you can use OnActorDead as a Workaround:
example:

public override void OnActorDead(int missionNumber, string shortName, AiActor actor, List<DamagerScore> damages)
    {
        base.OnActorDead(missionNumber, shortName, actor, damages);
        if (actor is AiGroundActor)
            GamePlay.gpLogServer(null, "missionNumber: {0}, shortName: {1}, Type: {2}", new object[] { missionNumber, shortName, (actor as AiGroundActor).InternalTypeName() });


        if (actor is AiGroundGroup)
            GamePlay.gpLogServer(null, "Groundgroup: {0} destroyed", new object[] { actor.Name() });

    }

you get for example:
Server: missionNumber: 0, shortName: 0_Chief3, Type: bob:Wagon.14T_Tank
Server: missionNumber: 0, shortName: 0_Chief4, Type: bob:Wagon.10T_Cattle
Server: missionNumber: 0, shortName: 0_Chief5, Type: bob:Wagon.10T_Cattle
Server: missionNumber: 0, shortName: 0_Chief1, Type: bob:Wagon.C_Class_0-6-0_tender
Server: missionNumber: 0, shortName: 0_Chief2, Type: bob:Wagon.14T_Tank
Server: missionNumber: 0, shortName: 0_Chief0, Type: bob:Wagon.C_Class_0-6-0
Server: missionNumber: 0, shortName: 0_Chief11, Type: bob:Wagon.12T_CoveredGoods_SR
Server: missionNumber: 0, shortName: 0_Chief10, Type: bob:Wagon.10T_Cattle
Server: missionNumber: 0, shortName: 0_Chief7, Type: bob:Wagon.12T_CoveredGoods_SR
Server: missionNumber: 0, shortName: 0_Chief6, Type: bob:Wagon.13T_5Plank_OpenGoods

So you can count how many Wagon are destroyed and if enough you can show a Message etc.

btw i found this in my log.txt
447] ERROR [VEHICLE] 0_Chief1 : Die by collision with crater
[447] ERROR [VEHICLE] 0_Chief2 : Die by collision with crater
[447] ERROR [VEHICLE] 0_Chief3 : Die by collision with crater
[447] ERROR [VEHICLE] 0_Chief4 : Die by collision with crater
[447] ERROR [VEHICLE] 0_Chief5 : Die by collision with crater
[449] ERROR [VEHICLE] 0_Chief0 : Die by collision with crater
[449] ERROR [VEHICLE] 0_Chief1 : Die by collision with crater
[449] ERROR [VEHICLE] 0_Chief2 : Die by collision with crater
[449] ERROR [VEHICLE] 0_Chief3 : Die by collision with crater
[449] ERROR [VEHICLE] 0_Chief4 : Die by collision with crater
[629] ERROR [VEHICLE] 0_Chief5 : Die by collision with crater
[629] ERROR [VEHICLE] 0_Chief1 : Die by collision with crater
[629] ERROR [VEHICLE] 0_Chief2 : Die by collision with crater
[631] ERROR [VEHICLE] 0_Chief0 : Die by collision with crater

May be this blocked the activation of the trigger?