Combat Commander gets your blood flowing.
The Rubbo translation is clear on this. The same constraints on what can be loaded apply to the total items on the wagon.
OK, that is what I thought but there seemed like there was a little wiggle room.
A player remains Loading Master until the Wagon leaves the city. If the Wagon remains in the city until the next turn, he may add more goods of the same type to the Wagon free of charge (no closed auction occurs), and may continue negotiating with other players if they wish to load their goods. The normal restrictions still apply (no more than a total of 3 of the Loading Master's goods on the Wagon, which must all be of the same type; no more than a total of 2 goods for each of the other players; players' goods may not match those of the Loading Master). In this case, if the Loading Master initially did not place any goods into the Wagon, he is now restricted to load a type of good that the other players did not already load.
Normal restrictions could apply to how many can be loaded on the wagon, rather than the wagon's carrying capacity.