Set the Range value for your artillery types to zero (in Object_Specifications table). Then they are immobile and must be transported by other units.
Alternatively, if you give them a short range, e.g. 5 km, then they will be limited to that distance of movement and will use up all of their supply doing it.
Thanks, Shades.
Sorry for very,very late answer. Busy.
So many possibilities....
I just found out that they increased the loadcapacity for the trucks in the campaign I am participating in
That and the reduction of movement for trops and artillery will do the trick