I had excellent luck using ground glass stopper bottles.  Mercuric 
chloric was added after the sample was collected.  Silcon grease was 
applied to the bottles.  THe bottles were then packed in especially 
built wood boxes with sponge rubber packing on the bottom and top.  THe 
lids of the boxes were screwed down.  The foam rubber applied pressure 
to the bottles and kept the seal intact.  Cardboard was placed between 
the bottle also to prevent breakage.  Samples were stored in this 
manner for several years with no measurable leakage.

Shipping by air, is another matter.  The lower pressure and cold 
temperturs of air cargo hold could cause real trouble.  All my samples 
were retuned to sea.  This was the GEOSECS program.