The 3500 DRW Mega cab has the same 9750 rawr as the other DRW trucks. It weighs 137 lbs more on the rear axles so payload in the beds are basically the same.
The Mega sits on a 160" wheelbase vs 169" for the crew cab x 8' bed. No difference there in ride or handling.
I made a living pulling heavier GN trailers than a rv trailer with short beds and long bed DRW LDTs. They both did the job just fine.
Just get a one ton DRW trucks in the bed length you need...in the brand you like.
Just make sure its the white one.