Soda is great for removing paint, no so good for corrosion. Be careful using the RoLocs, the heat from the friction will deform the aluminum skin also. I’ll get slammed for this but I use toothbrush size wooden Stainless Steel brushes on aluminum to remove corrosion. I use these ss brushes to clean aluminum before welding (TIG) as the bristles become worn the brush gets used on corrosion (once they get used for anything else they never get used on aluminum again). The Aluma-Prep is an acid (diluted) that eats the corrosion, on vertical surfaces you can use modeling clay to help control drips and runs of the aluma-prep which is applied with wooden cotton swabs (Q-tips). Use light pressure when scrubbing the aluma-prep withe SS brush, the solution will turn dark until all the corrosion is gone so keep cleaning and re-applying until it’s corrosion free. It’s not hard work but it is tedious….. as a side note aluminum starts oxidizing once it is cleaned so work only a few spots close together at a time, once a spot is cleaned get at least the conversion coat (alodine) applied, primer can be applied latter on (with in a few days)…. Read the instructions on the Aluma-Prep and Alodine, if your a little worried about damaging the surrounding paint with the alums-prep you can dilute it with water, but the weaker the solution the longer it takes to work