There are two end goals being pursued--remove any oxidized or fading color, make a gloss shine for the finish.
The oxidization can be removed with a variety of products. For me, the easiest is to use Jasco Prepaint Conditioner in a garden sprayer and brush with a long handled soft bristle brush. Sometimes, an additional spray of Jasco (diluted) is required. I've used this product on many different vehicle and non-vehicle surfaces over the years. It is now a non-TSP alternative. TSP will also work, as will any phosphoric acid based product. In a former career servicing sailboats, we used more intense acids to clean hulls. Unwarranted for RV's.
The shine can be applied with the myriad of waxes available. Boat/marine wax systems work well for fiberglass sided RV's. Floor wax leaves a durable shine but the synthetic, heavier waxes may crack and peel from road use or UV degradation. Vehicle waxes will leave a shine on even aluminum sided trailers. I am now using Parfe liquid wax. It is applied by spraying and leaves a fairly durable shine.