An option for a harmless filler is the Great Stuff brand gap/crack filler.
It gets used for backgrounds in cages and stuff, and silicone adheres to it well if you scrape off the outer shiny layer once it dries. I'd add the silicone to keep it extra water-proof, but some people have carved it and just painted with acrylic paints and had it work out fine from what I can tell.
Sent from my SM-G950U using Tapatalk
Reply With Quote