For the situation you describe, I normally use Reflectix insulation (available at the Lowes store locally in my area):
http://www.reflectixinc.com/script/products/product.asp?ID=72
I seal the lap seams with aluminum tape.
It's a LOT cleaner to work with than any fiberglass insulation. If most of your fiberglass wrap is intact, just re-wrap over it with the Reflectix.