Measuring Tow Bar Weight

I understand two ways of measuring the actual tow bar weight is to use a gauge or a set of scales with a piece of timber. Could you dispense with the timber and lower the nose wheel down on the scales. My thoughts are to set the caravan up level with the stays in position, then position the scales under the nose wheel and finally raise the stays to apply the load on the scales. My reasoning is because the only place I can take the measurement, is when the caravan is in storage, and the ground is not level.