A surge protective device (SPD) assembly module includes a polymeric outer enclosure, an SPD module, a first terminal, and a second terminal. The polymeric outer enclosure defines an enclosed, environmentally sealed enclosure chamber. The SPD module is disposed in the enclosure chamber. The SPD module defines an environmentally sealed SPD chamber and includes: first and second electrically conductive electrode members; and a varistor member formed of a varistor material and electrically connected between the first and second electrode members. The varistor member is disposed in the SPD chamber between the first and second electrode members. The first terminal is electrically connected to the first electrode member and extending out from the outer enclosure. The second terminal is electrically connected to the second electrode member and extending out from the outer enclosure.