Interesting thread on the Tesla forum towing an Airstream.

RCMAN46 wrote:

Did a little research and it appears the 34 kwh number the EPA provided does not take into account efficiency of the gasoline engine which at best is 30%.

What is your source for that huge mistake??
The calculations I saw were explicit on how they measured gasoline efficiency (using their huge database of existing car mileage reports). That seems better than any guesstimate of efficiency.