In the past I have found references to porch floor covers for porches on second floors and for porches that are built over basements. I have never found any clear directions about how to install or maintain such a floor.
TOday I visited the Cleveland Canvas Goods Manufacturing Co. (http://www.clevelandcanvas.com/) and they are familiar with using canvas for this purpose. They have a short instruction sheet for their reccomendations about installation and painting of this surface. I haven't used the approach yet but plan to, but this may be a resource for those seeking an answer to this issue.