Hello Alan
First of all 7% is not a rule it is only a guideline, and as it was suggested many years ago, it no longer adequately represents the current state play for today's outfits.
The law does set limits, and it is defined as the lower of either the cars tow ball limit or the caravan hitch limit. It should be noted that most normal saloon cars are limited to about 75kg. You should always check the figures that are specified for you car/caravan with your supplier or dealer.
The general advice is to arrange your nose load to be a high as possible (within the limits for your outfit), In your case it is 100Kg as set by the caravan manufacturer. but there have been some unsubstantiated reports that some caravans with a 100Kg limit have experienced some problems when braking. The suggestion is that the over run brake system is not as free as it should be because of the high nose load causing some binding on the actuator slide.
As other caravaners may have used the same model of caravan with cars with a lesser nose load limit (75Kg) without difficulties, I venture to suggest that provided the nose load is around 75Kg, then you are unlikely to experience any major problems.
If you do have stability problems whilst towing then by all means up the nose laod, but also check your tyre pressures and load distribution in the caravan.
DEL,
I am intrigued to know what vehicle you have that has a permitted tow ball load of 240Kg?