Our 2007 Monaco Monarch also has aluminum siding painted with automotive type paint. Has vinyl graphics. Had full front 3M covering installed at an independent shop two days after picking it up new in 2007.
After washing, I use automotive cleaner wax on the sides and back cap about three times a year(fiberglass top once a year). I don't touch the vinyl with car wax, but use 303 Aerospace Protectant every couple of months. Graphics look like new after six years as does the paint.
One of the reasons we bought this unit was because it had the aluminum siding. Our previous motorhome, a 2001 Itasca Sunrise was purchased new also, but after about three years the fiberglass gelcoat finish yellowed even though I kept it waxed. The painted aluminum siding is much easier to polish than gelcoat.
