I have a 400 hp Cummins pulling actual weight of 43,700 lbs including the Wrangler. It's no race car, but does great over the Rockies (my backyard). I've got an actual GCVWR of over 59,000 lbs.
I think rather than worry about torque and HP (the engineers already looked at that), you need to look at what is left on the GVWR of the coach, and what the actual tow capacity is, because it should be engineered with enough power for all of that. If it's already overloaded or close to it, and you drop a 12,000 lb trailer on the back, you won't be happy with performance.