SH hasn't ventured to the American Southwest, either. There are plenty of routes here which feature less than optimum maintenance. I have used various mapcases, including the ubiquitous ziploc bag for many years. In dry desert conditions, it isn't the rain that degrades maps, it is your constant perspiration which waterlogs the map,and everything in your pockets.

If I know I will be using a map extensively, I give it a bit of waterproofing compound and then precut it into sections, joining them with a good flexible tape. That avoids the wear and tear that occurs at the joins of an unprepared map. Due to some mysterious process, vital information is always obliterated, when you fold a map several times in the same way.

The waterproofing compound helps when you shave off the margins of the map to use for starting a fire. Multipurpose!