A look at the Monaco brochures
for the Monarch indicate that the 2003 year had aluminum side walls, not fiberglass. I believe the last year that Monaco offered aluminum on the Monarch was 2007, on the SVE model.
Our former Class C coach had a painted aluminum skin. The manufacturer recommended #2180 Ultra Polymer Sealant from Finish Kare. Here's a link
to the product's Web page. I found it was absolutely fabulous at removing light surface oxidation and restoring shine. Elbow grease is needed (I prefer not to use buffers, for fear of swirl marks). I use it on my cars now. I found no additional waxing is needed to keep the shine. Great stuff!