Wiper motor cover HELP!!!!

Well, after changing the speakers and covers on my 90, I noticed that the screws would not bite into the dashg allowing me to secure the speaker as over the many years the water leaking through has caused the metal on the inside of the speaker cover to rust. So I now am looking for a new wiper motor cover for the left side of my vehicle with the speaker hole. The part number is MUC1716 but i cannot seem to find it any where. Anyone got some bright ideas as to how I can get my speaker mounted there securely? Help is greatly appreciated.

speed clips/spire nuts? riv nuts?

Cheers for that I just glued some of the speed clips onto the foam on the inside of the dash and screwed the speaker in, not all of them tightened right in, but I think that it should be ok until I get to antother autojumble or something to get a new cover.