Q:

Anatomy of a chinese serpentine dragon?

In our world  there are two species of dragon that took different evolutionary paths due to environmental pressures. The first of them, called smaugs, are as large as a quetzalcoatlus, with a wingspan of 50ft and a height of 9ft. The second type of dragon, called  shenrons, has a snake-like body with six legs and a large, but undetermined, size. It also has wings, but due to its long shape, has issues with flying. 
What I need is a practical design of this creature. My first idea was modeling it off of a flying snake, which fan their ribs to double it's width and helps it glide. But as this creature is supposed to be large, this sounds stupid.
How can I bring this creature to life?

A:

Possibly it could have sacs which it could fill with some sort of lighter than air gas, and large fins and tail to give it momentum. Basically they would be swimming around in the air.

A:

Make em glide baby
True flight with a large creature is hard in principle, since at a certain weight animals simply can't generate enough muscle power for sustained flight,  since it requires even more muscle power, which requires more mass, which then requires more mass. Large animals like Pterosaurs cheated the system by having hollow bones, which allowed them to circumvent the mass problem while still being quite large.
So perhaps these Shenrons instead utilize a similar flight system to leaping lizards, where their ribs fan out to form web-like wings for the express purpose of gliding. they would not be true wings, but it would allow a form of flight for these massive serpent dragons.

They could launch themselves from high places in the same manner as Asian flying serpents (by forming a J shape), perhaps from cliffs or enormous trees, and glide down rapidly towards their targets, diving at them and wrapping themselves around their target like an anaconda.
Alternative option
Rather than giving them the same flight system as leaping lizards, you could give these Shenrons multiple sets of wings like those of a wyvern, which would allow it to not only grab onto trees, but allow it to glide without it being too awkward of a system.

Image sourced from The Genesis of Species - 1871
Info about Flying Asian snakes: http://blogs.discovermagazine.com/80beats/2010/11/23/video-reveals-how-a-flying-snake-slithers-through-the-air/#.XXHi1PZFyDs

