I have never used foam for mounting a box (have used plenty of mortar or epoxy for metal boxes in block) but I like the idea. A lot easier to apply than the methods I have used. Where I do use foam a lot is to seal penetrations into Sensitive Compartmented Information Facility (SCIF) areas. It is usually required by the clients we do service calls and build-outs for who are governments contractors and have to comply with Gov. Spec. to keep their contracts. In my experience, 90 percent of the time the only distribution gear in a SCIF is for IT so and circuits needed for additional equipment has to be pulled from outside the area. Keeps the feds happy I guess, and never have had any inspector bat an eye.
