All over the great white north, chest freezers are left exposed to the elements, many lasting 30 to 50 years in them. I think you should be trying to find out which freezer is particularly vulnerable to the elements, so as not to buy it, rather than thinking you need an exceptionally good freezer to keep out in the elements.
Also, don't entirely discard the notion of of a small indoor freezer. An entire (average sized, white-tailed) deer, properly butchered, will fit into three common "office boxes" (maybe 16x18x20). You should be able to pick up a chest freezer that will fit that, with total size only equalling that of a small dresser, for less than 200 bucks.