I have an '03 Ultimate Advantage. The clearance lamp lenses pop off. As I recall there may be a little place along the edge somewhere where you can get a screwdriver or knife blade in to assist.
While you are up there, take a good hard look at the gaskets under the clearance lamps. Mine turned to sponge rubber soon after we bought the coach new, and rather than keep rain water out they wicked water in. We had a windshield leak that I traced to a clearence lamp, and confirmed by removing the screws you see inside and finding they were severely rusted. You cannot get new gaskets without buying the whole assembly, so I sealed mine with silicone caulk, and have them on my maintenance check list to check and repair as needed twice a year. Interesting to note that my front lamps are attached with screws while the identical rear lamps are attached with pop rivets. Also, the gaskets on the rear lamps are in perfect condition ...they did not turn to sponge rubber.