I know this may seem unrelated but I am a substitute school bus driver.
A few weeks ago I drove a slightly Shorter than normal 2010 4500 Series Chev van chassis With a regular steel school bus body Bus. I'd estimate the weight right at about 11-12K lbs. (GVWR of 14,500lbs) This bus is a lot like a RV of that size and weight.
http://www.thomasbus.com/bus-models/school/minotour.asp
The digital dash readout said average 7.2 MPG and average speed of 16.0 MPH
Remarkable MPG for stop and go pickups, but it did seem correct. It had a 6.0L engine and was able to keep up with most any Car.
I can't imagine it would have problem towing a CRV around.