This is a study in its own...
Take a look at the videos I have attached. While more steel and larger vehicles may seem better, its all about crumple zones, airbags, and roof resistance tests.
Stay out of hummers, They have the worst crash test, have poor crumple, and poor roof resistance. You just have to sit back, do your own research and figure out what offers the best crash protection. Yea Mercedez is leader in safety but their side impact on the ML series was un impressive. VW has the Tiguan and it has very impressive roof resistance test including 15,000psi at under 2 inches of crumple, where most othr cars have already crumpled 4-6 inches at 15,000 psi. Ill give you some links to videos to get you started. I will admit I am impressed with the whole line of F series also the Sierra and Silverado's have made large strides in crash test ratings, leaving the Ram series behind.
Although your interested in DRW (duallie) I would not stop looking, single rear wheel truck (SRW) has less chance of loosing traction in bad conditions, its all about "GVW per Tire Surface Area" The more tire surface area you have, the less weight you are getting to the ground technically speaking. Duallies are not made for traction, they actually sometimes have horrible traction, they are made for comfort while towing large loads and to prevent trailer sway. Not to mention the 4.10 gearing and horrible fuel mileage whether it be diesel or gas.