With this box and the new comp it is very easy to fill the geltray with e.g. Agarose.
Just put the geltray in the preparation box, snap the comp in and fill the box with your Agarose up to the "max" marker. The height of the Agarose will be 11mm (0.43"), the gaps for your DNA samples will be 5mm (0.2") deep.
You need all parts from http://www.thingiverse.com/thing:103589 (except the comp), the preparation box and the comp from here.Gel preparation box for DNA Gel Electrophoresis Box by Bofferle is licensed under the Attribution - Non-Commercial - Share Alike license.