Originally Posted by orbywan
The question is this; you've aluminum skin over a steel frame. How do you keep dissimilar metal corrosion at a minimum or eliminate it?
Spend the rest of the weekend on Google and research the heck out of the topic.
Caulk and adhesives will be heavy, but will also have benefits of preventing air and water infiltration by sealing the joints.
Building paper (roofing felt) will also be heavy. Tyvek will be much lighter, perhaps it can be spray mounted to the back of the aluminum prior to mounting.
Sound absorption materials will be expensive in addition to being heavy, but also have attractive attributes such as insulative qualities.
Perhaps a double sided tape will allow you to mount, seal and separate the two materials without additional mechanical fasteners. Call up the 3M technical assistance people and see what they recommend.
You also have weird things such as "insulative paints " which may be an option worth researching.
You just need a "bond breaker", but be aware that moisture and condensation can transfer chemicals between the two metals allowing a small degree of migration. Not as much damage as bare contact, but nothing is perfect short of total encapsulation (epoxy paint?).