This is like a DAH moment.
If the load is within the vehicle's rated capacity, then load 'er up and go with it. The hypermiling tip is correct in saying the trailer is extra weight and etc. BECAUSE IT IS.
Overloading a vehicle is no different then overloading a TRAILER so don't do that either.
Who was talking about overloading anyway? Oh yes, that's right, nobody.
Sometimes the trailer is the best solution and sometimes it ain't. Wanna go through every possible load/vehicle/trip combo? My A.D.D. won't allow me to follow along.