I agree with you fully, John L, but would just like to add a few extra comments. When defining maximum permissible towloads, the manufacturers do not (normally) distinguish between caravans and any other trailer. Low loader trailers are inherently more stable so there is no reason why an experienced driver should not make full use of what is allowed. However, with high sided caravans, the situation is more critical. I refrain from saying what is the maximum that one could go over 85% and still be safe because, as you say, it depends on so many factors (the skill and alertness of the driver, the weather, whether the towcar is fitted with a trailer stabilising system, and so on).