I need to explain the piece that will hold the canopy in place on top of the box (which will be mounted inverted over the box when I'm ready to cast a mold).

I cut a hole under the canopy that will allow me to see the level of the silicone as I pour it. During the molding process I'll add water to the inside of the canopy as I pour the silicone around the outside which will equalize the pressure on the canopy to help keep it from deforming.

The OEM canopy is open at the rear and needed to be plugged. For this I cut and formed a piece of 3/4" hemlock to fit the opening. This plug will be glued to the canopy mount before the canopy is mounted. The portion beyond the canopy was rounded to help the plastic transition over the end without forming webs.