The best ones are made by you. The plastic ones add a bunch of weight and you still have to build the rails and such to screw it to. Keep it simple and put in a good set of rails and be done with it. I usually use 1/8" lite ply to make the tray then either use bars of 1/8" aircraft ply below for the screws to bite into, or 1/4" bass wood. Both work well. The same thing goes for the plastic servo trays.

Don