Peter, I finally found time to work on my flat panel some more. The main issue I had was getting the LED string to be dim enough to allow an almost full range of control. Binned 2x2 Red needed a low intensity setting while unbinned H alpha needed almost full brightness to get an exposure time in the range I was looking for ( 2-10 seconds). I ended up with a series of diffusion materials and a 2-stop neutral density filter (stage lighting gel) to subdue the light intensity. The device is held together with masking tape at this time while I sort out a way to easily hold the four main sub-components together.
As a cobbled together device with bits acquired from a range of sources and 3D printed components supplied by my son, I don't feel comfortable in offering to build you one - mine is sized for my GT-71 refractor so it's quite compact. If you decide you want to tackle building one I would be happy to share with you my circuit diagram, program code, and design considerations.