Looks like the previous owner of your trailer removed the classic molding, squared off the openings, and replaced it with some kind of trim. Like trimlok? Looks great, imo.
If you don't like the tambours ( and I can see why, they do take up storage space, and have a tendency to jam), you could easy return to the original sliders. A couple of pieces of track, cut new plexi, drill the thumbholes, pop in the grommets, and done. I actually like our sliders in our 2008. They're smoked plexi, which maybe someday I'll replace with some patterned plexi. And, probably not.
When we took