Aluminum Kool Seal is a good product that seals very well to aluminum. It is what Avion always used, and is what Dr. G (Donald Gradeless, the Inland Andy of Avions) still recommends. It's getting hard to find, though. I'm not sure if they're still in business. Lowes and Home Depot no longer carry it. Ace Hardware supposedly does, but I've not seen it in there either.
Looks like Panther Rv carries it.
Kool Seal Coating
Airstream always recommended Vulkem. And I see that there are cross references from Sikaflex to Vulkem products, so you're probably fine with those.
Last sealing I did was for my new roof vents, and I used a product from Dicor (Panther also carries them...I'm not an ad man for them, they just had the best prices on the vents and I got the sealer with the vents) that was made for aluminum and so far it's worked very well too.
Best of luck,