I was curious as to the difference a full rear water tank or the three jerrys made to the ball weight so as we packed the camper this morning I had a play around with the Towsafe Ball Weight http://www.campertrailers.org/towsafe.htm
Our Track Trailer Eagle is based on a 6x4 foot Guiding Star box trailer with a short 1050mm drawbar & a rear 60 litre water tank mounted behind the axle. The rack across the front holds three twenty litre jerrys. Water weighs one kg a litre.

With no water added the ball weight was 100kg. It was once a lot lighter before we added the two 120 amp hour AGM batteries weighing 35kg each forward of the axle in the battery boxes.
Filling the rear 60 litre water tank only makes the ball 110kg
One jerry full on the front rack makes the ball 120kg
Two full jerrys makes the ball 130kg
Three full jerrys makes the ball 140kg
If you are attending a weekend meet where we will also be, the Towsafe Ball Weight is available for members use.
We have not weighed the camper fully loaded since we put the new all 14oz canvas on, so we are dropping into a public weighbridge on our way tomorrow morning http://www.robcaz.net/new_canvas.htm