There is a slightly problem with how the cargo mesh is implemented (iron ore and coal). In the mdl file there is only a maxHeight value and then the mesh will transformed on the Z axis to just move the mesh upwards as it loads.
maxHeight = 1.9
This is fine if the waggon/cart has straight walls and a thick floor where the cargo mesh can hide completely when empty.
If the maxHeight value where to be a transformation matrix instead, and the loading process simply morphed from the original matrix to he load matrix. this would transform the cargo mesh as it loads, allowing us to have V shaped waggons/carts as the base can expand while transformed. It would also be easier to hide the mesh when empty because the Z-Scale would be lesser than on full load.