Mer is an "all in one" like Super resin Polish and Meguiars Ultimate Polish to name two popular competitors. They contain mild abrasive, cleaner, a filler/masker to cover minor scratches and swirls and a finishing product. The finisher may be a natural wax or synthetic product, but either way it will add shine, repel water and protect for several months. A dedicated finishing wax won't improve the paint condition, but once the paint is in good order a wax will add more shine/reflection and better protection for up six months. As Agger states, the choice is yours. Time is a big factor as caravans are large, so at the moment I have waxed the roof that receives the most airborne contaminates and merely polished the sides since buying it six weeks ago. Before winter I will re-wax the roof and wax the sides

Scotchbrite purple pads are used in the painting industry, you can polish out scratches left by the pads with cutting compound or tcut