I used some big self tappers when I did my speaker seals.
Having second thoughts about a rivet tool, as I`ve never needed one before I don`t think it would get much use in the future.
I have been to the dealers and ordered the Mk8 splash guards.
I've fixed a few VAG cars in the past just that when I got my rivet tool I made certain it could do decent sized rivet nuts..just its a big tool, so can be awkward. as the handles are about 18inch long!!