As somebody who lives in the city, but needs to travel 200 miles four times a year... I had thought of this concept before, albeit with a regular gas engine, not a turbine.
There is one big advantage compared to a plain EV: range!
And, there are also big advantages compared to a ER-EV like the Volt:
-reduced complexity of the vehicle itself
-reduced weight of the vehicle (no need to carry your gas engine around when you don't need it)
-might be quieter than having the engine in the car, and therefore it could run at constant rpm without annoying
"the average consumer"
Now, if a company started making those trailers using optimized gas engines like the one Lotus designed (very light, simple technology, durable, optimized for efficiency) {see
Lotus Designs Extended Range Electric Crate Engine} there would be 0 reasons why you can't have an EV as your primary and only vehicle!!!!