I don't tow "heavy" with the V-10 in my 2012 24' Class C but am here to tell you that V-10 is an awesome brake on the often long downhills. It is as much a function of the 5 speed Torque Shift transmission as the engine. I can cruise down a 6+% grade for ten or twelve miles and never touch the brake pedal. All that is required is to shift into the "Tow Haul" mode which locks out the 5 gear/overdrive. This holds the coach at 50-55 at around 3,000 rpm and the best part is we are not burning a drop of fuel!
If you run into more hill than that simply down shift into third (thus eliminating 4th gear), and the rpm will climb but the coach will hold at around 40 to 50 and you are again not burning any fuel. You can get much the same effect on older models (that do not have the tow haul option), by locking out overdrive. You will never harm a V-10 by inducing 3,000 to even 5,000 rpm... they are built to do that.
Don't buy into the nonsense that you have to have a diesel to get effective, efficient engine braking. I always laugh when I pass a rig who has been riding their brakes so hard that I can smell them. It's just s a shame they don't know how to drive.
:C