why not the option of drill and tap 5mm metal threads? I have used pop rivets in the past and have torn the whole track off and that was MK1,. I hate to see 2 up cos that's a lot of force.
Self tapers should not be used in metal or in the marine trade. They are not reliable. the heads break off and when you want to take them out the will break and you have to drill the out making a bigger hole. I deal with this crap everyday day.