Well I just happened to have had a Dodge mega cab, SRW 3500 totin' a (est) 32 -34 (maybe even a 36?) ft Cedar Creek 5er pass me on I-40 last week.
I pulled back alongside and as best (safely at 70 mph) as I could, perused the setup and it seemed to me that the end cap lacked about 2- 2 1/2 feet contacting the rear cab.
. I followed the unit, hoping that it might pull off somewhere before I had to so that I might get a chance to see things up close a little better, but it didn't happen.
That Cummins seemed to purr right along under no strain and having sat in the rear of a mega cab a few times, I know the folks in the back seat were sure comfortable.
As others have indicated, seems only logical that Dodge would figure this out in a year or two and go with a long bed.