Side mirror reinforcement plate rivets

[berndtj]

Kind of an odd question. The reinforcement plate is loose on my car and the passenger side mirror wobbles annoyingly. I took the door panel apart and the reinforcement plate itself is loose. The rivets no longer hold it tight.

My question is what type of rivet should I use? If I use steel, do I need to worry about rust? Will aluminum rivets hold strong enough over time? It seems like these two small rivets (1/8") actually have to hold a fair amount, and the mirrors will constantly want to vibrate, etc.

Any advice would be great!