Hi bearcat (as in scanner?), if the insulation is the foil backed stuff it will act as a very effective screen, downlead needs to go through it. It may be worth experimenting to see if the foil backed stuff acts as a good groundplane - anyone tried it? I once made a discone from a sheet of very thin stainless steel - superb performance, but was so lightweight, it wouldn't have lasted more than a couple of days outside.