I tow a 'big' Bigfoot
17 1993 with a 2011 Sienna and find it works well, better than my previous 2004 Honda Odyssey, mainly because of the automatic transmission shifting.
BUT, I also have installed the Airlift 1000 helper airbags in the rear coil springs and I do have to be careful on slopes and driveway ramps. Coming in at an angle cuts down on the scraping. FYI, I installed the Airlift 1000 airbags ($87 from Amazon) using ramp stands without removing the wheels in about 2 hours myself (I'm 70 and too heavy!). Some cursing and sore muscles but not a very difficult job. I used a hemostat (Spring loaded needle nosed pliers would work) to slide the clips up the hoses to the airlift bag inlet barbs - that's a bit tricky. No drilling, cutting, bending or 'real' work is involved. See:<http://www.airliftcompany.com/manuals/MN-445_60723.pdf>
I used a Tee joining the 2 hoses and fill to about 30 PSI.
The Bigfoot is pretty square fronted and my highway mileage, depending on the wind, drops from 23 MPG (27 MPG-US) to about 12 MPG (14 MPG-US).
I'm running pretty close to the maximum weight
recommended so I make sure tanks are empty and I'm not overloaded. Haven't had any problems yet, knock on wood!