I do this all day long (seems like!). The quickest way I've come up with is to have two versions of the same file, one portrait the other landscape. That way the guidelines (once set) don't have to be messed with. I simply work on one in landscape mode, then copy and paste to the portrait mode and rotate to match the guide lines. When finished, I delete the landscape file. Only adds a few minutes to the process. My habit for guidelines is to use four red lines that are longer than the width and height of the page, formed into a rectangle for the art area. That gets deleted of course. This works for files to be printed on office machines, not so much for professional print houses (which I never use). Hope this inspires a solution for you.