I recently purchased a 40' fifth wheel toy hauler, triple slide. The dry weight is 14,050 lbs., I figure 1000 lbs. of gear, my motorcycle is about 950 lbs., hers is 650 lbs. We try to two with minimal...
Sounds like the original owner is a card carrying member of the "Pulls Fine" club. I wouldn't go for anything less than one of the newer 350/3500 Diesel Duallies. But in your case, bigger could be better. But as mentioned, you won't know until you have an acturate weight on that beast.