Need a 3500 series monster truck for a camplite 6.8?

I was building my dually on Ford site and don't remember the dually adding that much to the price. New dually makes 16-17 mpg empty or 12-13 with 6000lb camper, so higher fuel consumption is not an issue neither.
The only bummer for me was that dually did not have lockable differential option that SRW do. Had to buy LSD.
So IMHO > even if you only "think" the SRW might be marginal - get dually and don't look back.