I wish the supply trains/convoys were spawned out of an actual depot, instead of the building at each end of the route that we have now. Something that is very similar to the depots of WWII would be 1/8 to 1/4 of the city size we have now, with track or road along the outside perimeter. It might also be populated with factory objects, as well as auto-defensive guns.
EDIT: Also, why not allow players to spawn resupply from the depot? Not tanks, but M3s and C47s?