Peter: I have about 60 shippings with heatpacks and all went well. The important issue is that the shipping won’t last for more days than the heatpack can give heat. My heatpack normally give heat for 24 hours, but I think you can get heatpacks for 48 and 60 hours. I think the shipping cannot last out of these hours in winter, the styropor boxes will soon be cold (bad english)
My heatpack had a brutto temperature of 50 degree C and netto 30 d.C. The receiver measure the temperature and normally the water temperature hold from 20-25 d C
I use very small styropor boxes; 40 x 25 x 25 cm should be ok for 4 or 5 P
I have no problem sending fish in Norway, but I think sending abroad could go wrong because of the shipping period
Hope you understand this
Svein