glass break requires two UV channels to be available on a model file and secondary UV channel to have some ordinary (projected from front or top or side view) mapping layout. Additionally, collision object associated with window should have correct ID values set on polygons (I can't remind exact values, inspect original game model). And finally, chassis model's collision should have proper ID value on polygons that relates to window and doors. This specific ID value tells the game to let player pass by and let bullets fly through chassis collision on these particular polygons, as "some other collision model will take respond to this action" (allowing window to take proper respond if it's not yet broken). If I'm not mistaken, value of 2 is "pass through", inspect original game model as a reference too.