Would you consider a boardwalk? They're quite common in parks here in SoFL,
where it's often humid (if not pouring rain) and the sun is very strong.

Instead of wood, you might consider using an amalgam of recycled plastic and
wood. (Sorry though, don't know a resource for this material.) Wood is
high-maintenance in this environment and needs to be treated every year or
two with chlorine and strong preservatives.

Rhea Tannenbaum
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http://pages.prodigy.net/rheat1/natur001.htm
A unique signage system for living animal exhibits in nature
centers, zoos and aquariums. Modular, water-resistant,
scratch-resistant, easy to mount and remove.