Great post, thanks for the input! Its very helpful.
Those SS washers look like they'd do a better job. Where did you buy those SS washers?
Also, if the screws are not SS, I'd keep an eye out for galvanic corrosion that can occur between dissimilar metals that are in contact. Hopefully the paint on the screws is enough of an insulator to prevent the current flow. You might consider painting the SS washers as well, just to be sure.