Towing is the hardest thing you can ask of an EV's range. A caravan adds mass, but the bigger penalty is aerodynamic drag: a big box behind the car dramatically raises the drag the motor must overcome, and drag dominates at road speed.
As a rule of thumb, expect towing to cut range by something like a half, and to slow rapid charging stops into your journey planning. Only tow-rated cars should do it at all.
Our journey twin lets you add the effect of extra load, and the car pages flag which models are tow-rated. If you tow regularly, the honest advice is to plan around the reduced range rather than hope, see methodology for how drag is modelled.