Hello Tim and all
Nose weight is important, as you demonstrated to yourselves, but you do have to watch that you keep within the limits set by the car and the caravan manufacture, selecting the lowest of the two as your top target.
It is also important load the caravan safely and to check your tyre pressures are correct. The car should be set to pressures for maximum load.
As for stabilisers, they must always be considered as a top up rather a cure for instability. Your outfit must be stable at all normal towing speeds without a stabiliser; if you cannot achieve that condition, then you have an unstable and therefore an unsafe outfit - which would be considered illegal.
It would be unwise to accept the Report from What TowCar.com as gospel. It may be a reasonable guide, but only real life experience of the outfit will confirm its true abilities. - and driving style has almost as much to do with stability as the simple combination of weights and engine power.
The suction effect that occurs when vehicle's pass, is not fundamentally instability. It happens with all outfits to some extent. What can happen though, if an outfit is close to its control limit, the act of passing may cause instability to be triggered.
If you are that close to the limit, then you should slow down and drive at speed at which you can maintain full control regardless of what you pass, or what passes you.