First, who do you envision using the bed? Adults? Children? Yes, the bed will absorb humidity and feel damp. Is this, realistically, what you would want to sleep on? While the idea of a swing bed is fun, its practicality is limited. Will people actually use it to sit upon when simply lounging on your Porch? Or will they avoid it for fear of spilling drinks, or not having something to lean back against? There is a whimsy to the bed that I appreciate....and then there is reality of everyday use. Don't want to be a "Debby Downer" here, but.... think this through.

I think a regular porch swing and/or a regular day bed would make more sense.