Hi Rosemary~
I sometimes get rolls of the Priority Mail tape
from my clerk, too. It is quite flimsy- not like the normal
packaging tape, so I don't trust it too much. I usually use the
regular packaging tape (wrap it around the box both ways a couple
times, and along the sides so that no sand gets in the cracks), then
I'd go over that (around the middle of the box either way, but not
along the sides) with 1-2 layers of the Priority tape. If I only
used the Priority tape, I would wrap it around, like, 4 times.
Maybe that's going overboard but I know those boxes really take a
beating and I'd rather be safe than sorry! 
The packaging tape companies must make a killing off of people like me... 
