I question the value of a double wrap of tape. The second layer of tape doesn't seal it up better (I think), it just makes the (double) membrane over spoke holes stronger to withstand more pressure. You only need to worry about high pressures if you have skinny tires and/or are heavy.
Having said that, sometimes the thickness of double tape makes the tire bead/rim interface tighter, and that's what you need. But when you tighten it up that way it makes tire mounting harder.