With regard to getting the weight over the axle; the moment of inertia is the thing that causes the snaking or pendulum effect and is the weight of the object multiplied by the square of the distance from the pivot or axle. So put the weight 2 feet away it's 4 times, 3 feet 9 times, 4 feet 16 times, 5 feet 25 times, 6 feet 36 times, and 7 feet 49 times.
Putting something at 6 feet instead of 4 feet more than doubles the effect. In practice anything heavy within 4 feet of the axle is fine so that gives an 8 foot length in which to load the heavy stuff.
In a rear entry Dandy, even the gas box is no more than 4 feet but in the big Dandy with a loo it's got to be 6 or 7 feet so would be best not to load it too much.
My caravan is 18 feet body length and everything heavy is put close to the axle by Bailey the manufacturers. That's spare wheel, battery, heater, water heater, cooker, fridge and it tows very stable. This one was fitted with an Alko stabiliser and is the first stabiliser I've ever had. I have forgotten to clamp it down when hitching and must admit it does feel a lot tighter and stiffer with it on.
I take the view that the stabiliser disguises the onset of a snake so when it does it's difficult to control but this van has never snaked for me. I used to have a motorbike and sidecar which had a damper for the steering. Solo it had to be off, but with the sidecar on and no damper, the handle bars very quickly started swinging from side to side. The damper soon took that out so maybe they do work.
My previous van had no stabiliser and yes, I would get the beginnings of a snake occasionally but it soon stopped. My father had a caravan and that used to snake violently at about 35mph. That gavehim a lot of earache from the passenger seat.
I have experimented with various nose weights and find with too little, the whole thing becomes very floaty and unstable. Similarly, too much weighs the back of the car down and makes the steering very light.My van is 1326kg max weight so 7% is 93kg and 4% 53kg. I find I end up with around 50kg and that feels very stable.
The caravan manufacturer imposes a noseweight limit of 100kg and the car is 75kg I think so I must use the lower. Dandy don't seem to quote a maximum, but their chassis are so strong, perhaps there isn't one. I understand you can even jack one up using the corner steadies, something you would never do in a caravan.