Amazonia is not technically waterproof; when it gets wet it turns lighter but pretty much fades back when it dries. I don't know what its durability is in relation to cold temps but in general, after 5-7 years of regular use, it will start to yellow and crack, first in the bendable areas. The wipes and other latex sprays help maintain it but I don't know that the yellowing/cracking is preventable. Would love to know if anyone has an old Amazonia bag that has not shown these signs of age...
I use non-H bags for bad weather, but, if I had to guess which leathers are most weather-resistant, I would say buffalo and epsom.
I don't use the rain-kits, but I do tuck a garbage bag liner in the bottom of a bag if I think there is a chance of rain.