I my experience silnylon is a dirt magnet and since it's not truly waterproof water under pressure will seep through. But then again you're talking about dry climes.

I had good luck with one of these last year. It's incredibly strong for its weight. But that "talcum powder" dust does stick to it.
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If you only travel on sunny days you will never reach your destination.*

* May not apply at certain latitudes in Canada and elsewhere.