Towing Issues: srw vs drw, rear axle assembly, wheeled vehicle

Question
I frequently tow a 7000# utility trailer and a 12000# skidsteer trailer - I am looking for a new truck to handle the task. Currently I use a 2000 chevy 2500 and this does ok. I am looking at either a F350 or the Duramax 3500 I need to know what the advantages and disadvantages are between a dually and a srw Thanks

Answer
the advantages of a dual wheeled vehicle is that you are allowed a greater axle carrying weight when going across the scales.  
Now this may not be a factor for you, but if it is then you have a " MORE LEGAL " unit.

Now another factor is that you have a more stable rear axle assembly with 4 tires on the ground verses the 2 tires.  

I have a F250 and ford uses the same axle assembly for the F350 with the single wheels. Ford has gone and made a heavier platform to work with and allows it to be rated lower and still be under what it is actually rated for .

I hope this helps