I bought air shears, but it turns out my little pancake compressor just wasn't strong enough to go more than 6" at a time.
I took a staring break.....................to stare............
I ended up using the jig saw after attempting tin snips (don't do that). The cut itself was great, but the trail of scratches, not so nice.
Lesson learned today? Vertical cutting is stupid. Next time sandwich everything that needs to be cut - paneling, plywood, aluminum - and cut it all together on the ground, glue the aluminum to the wood while horizontal as well. That just makes more sense and would be a lot neater.