A BT Cruiser is a nice and very popular rig. One of Gulfstream's better products, I think. You will hear mixed reviews on Gulfstream as a manufacturer - some people have had lots of quality problems and poor support from Gulfstream, but there are others who are perfectly happy. In general, I think the Class B buyers are happy, though.
The Ford V10 is the standard gas engine in full size pick-ups and vans and so is the base engine for the Ford chassis under the BT Cruiser. I would guess you would see at least 8 mpg in that size/weight class and more likely 10 or even a little better if you avoid a heavy foot on the pedal and keep highway speeds down. Wind resistance increases with the square of speed, so a few mph extra can really increase engine loads and reduce fuel economy. You don't need to drive around at 45 mph, but you can usually improve economy if you do not try to keep up with the 75 mpg freeway traffic either.
