Lee Valley sells some LED lighting systems similar to these, with purpose-designed aluminum extrusions and diffusers. I don't mean to suggest that they're necessarily nicer than what was put together here, which is very neat work indeed. However, it may be a little simpler to work with a purpose-designed system with matched components.
Here are some quick links to the
aluminum channels and diffusers and the
LED light tapes and associated electronics. The corner extrusion looked particularly interesting to me; I might give it some serious consideration if I ever do some significant refurbishing/refinishing of my motorhome interior.