Hi John L. This topic has cropped up before. True when a caravan is added to the back of a car or van the weight is increased and the traction is better. That isn't the whole story though. The weight of the engine over the wheels of a front wheel drive car is still considerably more than the weight of a caravan on the back of a car, even allowing for a minimal shift in center of gravity. I don't drive many cars that are rear wheel drive, but have quite a lot of experience of rear wheel drive vans. In slippery conditions, laden or not front wheel drive vans offer better traction. You do correctly point out that much depends on throttle control and gear selection, but rear wheel drive in slippery conditions, I find particularly difficult to control.
Imagine, a slight incline, you are waiting at traffic lights and there is a fresh layer of snow/ice on the ground. When the rear wheels start to spin, not only does forward momentum suffer, so too does sides ways movement. You will often see rear wheel drive cars move left to right when the wheels are spinning, with front wheel drive, it is much more controllable, the power you put to the wheels generally goes in the direction you are pointing it. I am perhaps not explaining this very well, but believe me, rear wheel drive, great for going fast, front wheel drive for going slow. The added advantage is that the chances are that the front wheels are closer to the hard standing/road than the rear wheels when trying to tug the caravan of the pitch, every inch counts (apparently).