I have done a lot of repaints and work on frames. After I removed the dent I used nitrostan puddy right on the paint, no need to sand off the old paint. It is used by car body repair people to fill scratches. It sands glass smooth. Do not use Bondo. The dent will come out easily as the aluminum is soft and thin. Nitrostan comes in a tube and is very inexpensive at body supply shops. Put it on thin. Mask of the area that you are going to work on before you start. When you are done just paint a band around that area and add a decal.
Ed