A Ford E-350 will tow 10,000 lbs. when equipped with the 6.8 L V10 or the 6.0 L Powerstroke diesel.
See the following PDF file for the 2009 Ford towing guide.
http://www.fordvehicles.com/assets/pdf/towing/09_TrailerGuide.pdf
IMHO, Sportsmobiles are no more expensive than RoadTreks. One can...