You can get structural, closed end aluminum pop rivets, and that's probably what I'd do, but mostly because I have all the tools for pop rivets. If you have a Harbor Freight close you can get a structural pop rivet tool for about $25 I believe. Solid rivets aren't that hard to do and are probably the correct thing to use but you need an air hammer with the right head and a bucking bar to do it. I don't think I've ever used drive rivets as fishlessman suggested but my interests are peaked!