I've had a few of these in use for a number of years now, some are left mounted outside 365 days. Having quite a bit of MDF laying around all the time led to this relatively simple solution. The photos are from the first box were i just cut a simple oblong shape to fit in the box. The boxes have four stand off posts that will accept an 8G screw. In the first three photos you can see an ECG-P12R mounted along with a DC-DC controller. The MDF is 6mm thick, the screws used on the mounting posts should be recessed into the MDF to ensure no shorts on boards mounted directly to the mdf. a closer look, the white stuff under the edge of the P12 is just some double sided tape to keep the P12 flat. Now here's the template shape i cut out for all the later boxes. I just trace around it and cut out with a jigsaw. I hope this helps somebody. I have noticed that these boxes will over time not close cleanly along the top edge but a bit of gaff tape fixes that and really once you close them up for the season you rarely open them up.