Another option if you don't get many replies here, is to try the Escapee's forum.
http://www.rvnetwork.com/index.php?showforum=32
There are lots of people over there that use their HDT's, with a Smart loaded on the bed, and pull a 5er behind that. There is also lots of useful information (licensing, insurance, bed designs, pictures, etc) in their resource guide.
http://www.rvnetwork.com/index.php?showtopic=88214