I used steel zinc plated rivnuts to fit the bodywork. I put a bit of Sikaflex around all of them before crimping. So they also are a bit bounded too and not only crimped (which will make them even more difficult to get loose) and I believe it makes a protection layer/sealing. The excess is easy to clean with alcohol afterwards. It cheap too.
2014-07-08_10-28-13 by
Voucht71, on Flickr