The hitches are often used with large RVs at the upper end of a 1/4 ton or 1/2 ton pickups range and recently they have become popular to be able to hit the max tow rating for larger crossovers.
http://www.etrailer.com/Weight-Distribution/Curt/C17051.html
but there are a few options for smaller trailers such as this one:
STEADi-FLEX® Light Weight Distributing Kit w/Shank, Built In Friction Sway Control & Hardware, 4,000 lbs. (GTW), 250 to 400 lbs. (TW)
http://www.reeseprod.com/products/weigh ... 0m2XWmdIti
you can see from the below ad from the 70s, it significantly reduces weight on the rear tires. to the point where in this case they took off the rear tires for this photo ad.

I have one hooked up on the 21ft enclosed car hauler and it makes a world of difference when pulling with a 2013 F150. I would imagin there are a few trailers out there that would benefit from this setup on a tnttt scale.
Thoughts?