Thanks for the welcome Joe, main problem for the large fifth wheelers is the lack of larger trucks in the "ute" range [utility truck or pick up as you call them] on the market here. I am pulling the Hemisphere with a Colorado crew cab. It has a 2.8 litre Duramax common rail turbo diesel which puts out 470 Newton metres of torque, and pulls the RV easily. Our problem is the "gross combined mass" of the truck and trailer combined which in my case is 6tonnes [6000kg] and is the limit in my case so I have to be careful as to how much weight I put in the RV.
This is basically the reason why the aren't so many larger 5er's here.
Hemisphere lite 246RLBS
2.8 CDT Duramax