Dissimilar metal contact is always a problem and water makes it worse. Since aluminum fasteners are a non starter you make the best alternative choices. SS is a good start, SS coated and waxed is better, there are better coatings available but the cost goes up. The retention features of nut plates does not help the problem because it likes to wipe/scrape off the coating we just spent a lot of money for, which brings me the the issue of Aames prices.
Below is a copy of my last invoice from them for 6-32 and 8 32 x .500 SS coated and waxed. Average cost about $.45 each in quantities of 100. Torx is expensive always (China does not make them yet) SS is always double or triple the cost depending on grade, Coatings are always an added cost and waxing is more still. Are they worth $.45 each? Ask someone that tried to drill out a stripped Phillips head screw without damaging the pieces being screwed together.
I'm not promoting a senseless argument about value, it always in the mind of the beholder (screwer)

I have no more to say on this topic.
Thank you for your order.
========== GENERAL INFORMATION ==========
Company: Aames General Store, Inc.
Email:
Sales@AamesGeneralStore.com
Phone: (714) 838-3575
Order date: 8/21/2017
========== ORDER INFORMATION ==========
Payment By: Visa 4XXXXXXXXXXX2955
Status: APPROVED - 021839
Purchase Order: 794
Order: OnlineOrder_00025253
Product Name: Qty. 100-#6-32 x 1/2, MS Machine Screws, Torx Socket Drive, Flat Head, 18-8 Stainless Steel, Black Oxide & Waxed, RoHS Compliant, Torx Socket T-10 Driver, 82 Degrees Countersink, Machine Screw, Full Thread, DIN 965 Type
Item#: 7040TF2553
Unit Price: $42.28
Quantity: 1
Shipping Method: USPS Priority Mail Flat Rate Box
Product Name: Qty. 100-#8-32 x 1/2, CS Machine Screws, Torx Socket Drive, Button Head, 18-8 Stainless Steel, Black Oxide & Waxed, RoHS Compliant, Torx Socket T-15 Driver, Cap Screw, Full Thread
Item#: 7041TF2585
Unit Price: $47.43
Quantity: 1
Shipping Method: USPS Priority Mail Flat Rate Box
Shipping & Handling: $14.10
Grand Total: $103.81
Special Order Instructions
Please ship in USPS small flat rate box.