After four years and 30,000 miles of towing near my F-150s max cargo limit, I have replaced the shocks and I am considering a set of air bags because the tail seems to have become a little soft.
Unfortunately, while this may stiffen the suspension and smooth out the ride, it does not change the axel, max cargo, or any other weight rating. 
It should make the TV a bit less springy. 
Other then the softer tail issue, this combination was never let me down, AZ dessert travel, the northern and southern Rockies and all over the Midwest the e-boost has been as advertised.
A larger or different tow vehicle could provide more cargo capacity but since this combination works and we have never found a more suitable floor plan, we are not likely to change any time soon. 
good luck