I want to install a ceiling fan outside under a porch. I would run new conduit up to the underside of the ceiling joist. The joists are covered by bead board which I could cut away from the joist. I found a box by Garvin, their 54171-FANNBWP. The instructions indicate it can be mounted directly underneath the ceiling joist. It is a fan rated, outdoor rated electrical box. I wanted to get some experienced opinions on whether this would be a problem.
The only real reason to cut into the ceiling would be if you needed to bring the wires down from inside the ceiling. Since that isn't the case, I would buy some 3" lag bolts with pan heads (something like this) and drive them through the bead board and into the joist.
The reason for the diagram is they want to emphasize the joist part (#2 in the list). Screwing this into bead board only would be a recipe for disaster.