Interesting thread on the Tesla forum towing an Airstream.

I did some calculations.

I used $2.25 a gallon for gasoline.

$0.15 a kilowatt hour for electricity.

From the article 687 wh/mi for one leg of the trip while towing.

Divide the 2.25 by the .15 to get a gallon of gas equate to to kWh.

I got about 15 kWh.

Divide the 15 kWh by the 687 wh/mi I got about 22.

Thus the mi/ gallon of gas equivalent is about 22 mpg.

The best that the article mentioned was 500 wh/mi without the trailer.

Thus about 30 mpg gas equivalent.