I followed Monte's seat covering tutorial and had great success. As with many things, the process is a learning one, and would be much easier to do a second time. My only advice would be to stretch that cover down as hard as possible for a tight fit. A little bit of a wrestling match. Make certain the pan is clean and if you aren't using edging, take the sharp edges on the pan down so the cover will slide over them. Good idea to have someone there to assist you and hold things down. And to get cold beverages of course.
Other than that, just follow Monte's lead and you won't be sorry.
Steve