When you talk about aluminum siding I'm not sure if you mean a specific option related to your model, but we have a Milestone with the typical (these days) "sandwich" wall panels, with a foam core and aluminum skins. You can see metal shavings if you drill holes. This is all foam-core but I installed four Solera toppers from Amazon (yes, we have 4 slides) all on that skin and had no issues at all. They're installed on brackets that you attach to the walls first, so they're easy to hold in place. Each bracket has a ton of screws to share the load and the top rail does, too. If this is the type you have you should be fine. Be sure to drill appropriate pilot holes first, and use a hand-screwdriver to avoid stripping the screws.
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