IP protected Enclosure and Conformal Coating
There are different types of silicone adhesive, if worried about corrosion they should avoid acetoxy (smells of vinegar) or oxime (gives off MEKO which corrodes copper and brass).  They should use an alkoxy grade (gives off alcohol) or a one part addition cure - no by-products of cure - cures anaerobically, but will require heat to cure and adhere on just aluminium this would be the optimum choice.