You know, I caught the trailer bug about 2 summers ago now. We started towing our little Nomad 173 which weights in just under 3000 pounds with all our stuff on board with a Nissan Quest.
It's a 2012 model with the 3.5 V6 that Nissan puts in everything. I think in it I could 13 to 14 mpg at 60 according to it's trip computer.
But, it was the WORST driving experience! It felt like a boat rocking on the water everytime you hit a bump.
I finally got ahold of dedicated 2006 F150 with the 5.4l in it. It's been night and day. I only get the 10 MPG that everyone else has stated, but man it feels better for me and the kids!