I don't think the thickness of the wood is critical , but I do think it would be sensible to carefully consider the use you plan to put it to , then add some for the unplanned events
The decking on my pickup is 28mm , because that is what I was able to achieve. It is a Malaysian hardwood , because that is what was available. Oiled up it looks fabulous and is durable enough to see the trucks life out too , I think.
