What would be the strongest way to fit US boxes to mount a foil, like this

Thinking to epoxy 10mm divinycell/pvc foam? around the box and leaving the divinycell long enough to epoxy it to the underside of the deck like you would a Power or Tuttle box ?
Or would the conventional way, ie rout out a slot, line the slot with glass, fit Us box and glass over the top be strong enough?