Okay, I admit it, I'm definitely guilty of 
flattening Priority Mail boxes and sealing the 
ends shut for shipping cels.  Since I'm about to 
be shipping a bunch of cels out when my auctions 
end, I'd like to solicit comments on what people 
prefer for shipping.

Here's how I usually ship cels:

I take the smaller of the two big priority mail 
boxes and cut off the flaps at each end 
(otherwise it won't fit into the larger priority 
mail box).  I put the cel in the smaller 
flattened box and tape the ends shut.  I then put 
the smaller box into the larger flattened box, 
and seal the ends of the flattened box, then tape 
them.  (Add labels, write "do not bend" 
everywhere, etc.)

The reason I ship that way is because:

1.  As someone who's seen 1-layer Priority Mail 
boxes sliced by the post office, I feel that 
double-boxing is a must.

2.  I'm extremely paranoid that the ends of the 
large box may get sliced open if I only taped 
them shut and didn't use the adhesive strip.  
("Hey, I got a box, but no cel in it!")

3.  Priority Mail boxes and tape are free, so my 
materials costs are zero.

Does anyone have complaints or better suggestions 
regarding this method?