I had always been worried about the silicone and plastic.
Rick
Whe I first read this I thought it was about silicone not sticking to the PVC electrical box I tried using
WELD-ON #16 CLEAR MEDIUM BODY SOLVENT CEMENT to attach a small piece of plexiglass ( I do not know if it is acrylic or polycarbonate) and 2 pieces of 1/2 inch cedar ( end grain, and side grain) to a Carlon PVC weather resistant electrical box. It took a lot of force to break them loose, and in fact, the wood failed, not the cement. It certainly gives the joints a cleaner look that a bead of silicone.