There are moss walls in several of the Tropica www tanks - all of them done with stainless steel mesh and fishing line.
You are right, this can stand on its own buried slightly in the bottom-layer. It is very easy to gently lift out the entire set, for cleaning and/or trimming. A good way to thicken your moss wall is to press the long branches of moss back at mesh and re-tie with fishing line. Pressing the moss downwards initiate better branching. Be aware, though, that fish may try to go behind the mesh, so either leave room for that or try to press tight to glass.
Also note, that creating a decent growth at especially top corners require a light-source that actually reach these places. This may call for something extra in many "standard" tanks.
You may want to use Taxiphyllum 'spiky' instead of Taxiphyllum barbierii (standard Javamos). It is every bit as tolerant, but has a "thicker" appearance and branch out better.