I don't have tie-downs, however, if I decide that this is something I will for sure do, I'll likely pick up a set. I've toyed with the idea of a truck camper for a number of years now and never pulled the trigger on buying one. I can either save the tie-downs for later or resale them when I get back. I do have a plug in the bed though for hauling cattle and other trailers.
No, the truck isn't a Dodge Mega-cab. Its a standard Quad-Cab short bed that I converted to a dually using a Mega-cab bed and dually components (axle, front adapters, etc.). I have no doubts about the truck being able to handle the weight, just not sure about the whole LWB/SWB issue.