of any wire from deterioration from contact with the elements is to grease the ends of the wire prior to compressing the connector. Heat shrink material is better with the internal glue then without but using a self adhesive tape prior to using the heat shrink will work just as well. The idea of the heat shrink is not to keep the elements out but to keep the grease in. The grease will keep the elements (we're talking salt and moisture here)away from contact with the copper wire but grease will go away with time. It will dry up, get rubbed off and get wiped over onto other surfaces unless it is protected from doing so. That's where the shrink tubing or self bonding tape comes into play. Prior to retiring a few years back I was the supervisor in charge of the switch yard at a nuclear power plant on the West Coats. We routinely replaced wires as large as 750mcm and larger. These lugs were filled with a grease at the factory and came with a plastic plug for shipment to hold it in. I've made up hundreds of these connections over many years and I can't ever remember one failing. Many of these connections were directly buried in the ground for substation grounding grids which last for many many years.