Tesla's "problem" is that they are so efficient to begin with that any little deviation from nominal can appear to greatly reduce the range. It is actually not the Tesla that is missing the 'listed' range ('listed' range is actually the EPA range as calculated/measured against a US Government standard). It is actually the deviation or inability of the driver to drive within the parameters of the standard that reduce the range.To be fair most other current EVs vendors get their listed range (or actually noticeably higher in the case of Porche). Tesla seems to be the only current EV vendor with “optimistic” range statements.
This issue came up when the Prius came out. Drivers who were meticulous about their MPG would grouse about how running the Air Conditioner on their Prius cost them 10 MPG while on their previous car, it only cost them 2 or 3 MPG. The Prius still got better MPG than their previous gas guzzler, it just looked worse if you only focus on the effect of the deviation from 'normal'. When you think about it: If the Prius used zero gasoline to drive then all of the fuel used would be to run the Air Conditioner so it would look like the Air Conditioner would cost infinite MPG with the Prius.
Essentially if normal driving doesn't use much energy, other things will look like they take a lot.
Inefficient EVs such as the Porsche, will not be affected as much be deviations.
For towing, one is going to need some amount of battery KWh for the towed vehicle. This will vary with the aerodynamic efficiency (Cd), size, and weight of the towed vehicle and is pretty much independent of the tow vehicle's needs. It should be possible to compute the KWh/mile of a trailer and compute its range compared to the battery in the tow vehicle but, of course, trailer vendors don't provide this info.