I couldn't find a Conditionstate that is similar to the TransportContain behavior tag.
You could have a try with ConditionState CARRYING or GARRISONED.
Those are the only 2 that reference that something is been transported or contained. But i don't have high hopes it will work, to be honest...
I doubt GARRISONED will work because it is used in relation to buildings. CARRYING sounds promising though, even if it just changes the model when it is carrying any number of units. Thanks Flyby.