I used aluminium rivenuts with stainless countersunk screws (so no nuts underneath).
Single sided SA neoprene applied to the strips to prevent water getting between the strips and the running board. Easy to remove when required.
A good solution!
To pick up on Jay's very valid point, given there is next to no load on the screws then I think I'd use PEEK rather than stainless. PEEK cannot react with anything metallic. It is good to 180C which is far hotter than the outside of the silencer.
