Charging efficiency isn't 100%, so you'd have to tow it further than the range you need. Seems like it'd make more sense to just tow it to a charger.
That's not how it works. You basically get 5 mpg or less on the truck, while the car charges at significantly higher rates than the speed of the truck (in mph), because the car is more efficient at using the energy.
https://insideevs.com/news/514727/tesla-towing-70mph-fast-ch...
Towing at 70mph in the above example was charging the car at 65 kW. That's equivalent to ~260-270 mi/hr of charging rate assuming 250Wh/mi.
Distance wise, tow charging makes no sense. Energy wise, maybe it does.
The key here is that when towing (as opposed to going downhill) you can put much more energy into the motor generators per mile than is required to drive a mile. Due to charge/discharge losses, for your example this would have to be > 4x the amount. This obviously assumes the EV can regen at high sustained rates and you have a powerful tow vehicle.
So yes, you're right. The energy/distance argument should be one and the same.