As soon as you stop polishing, the aluminum starts to oxidize again.
depending on the product you use to polish, it will take more or less time before you need a complete re polish, but eventually it will no longer be shiny.
The nuvite is supposed to last a long time but I haven't' tried that yet.
I've been waxing my trailer since I started polishing and it keeps the shine along time. Regular car wax works for me.
1977 Safari Land Yacht
2005 Toyota Tundra SR5
2010 Ford Flex Ecoboost