I just recently got the Polaris Slingshot and i am loving it, How ever it is very hard to see who is behind me.
And the Slingshots do not come with a Rear View Mirror.
So i purchased a Mountable light weight Mirror off Ebay and printed a Mount to mount it.
Mirror can be purchased here: https://www.ebay.com/itm/Universal-290MM-Wide-Flat-Interior-Suction-Cup-Rear-View-Clear-Glass-Mirror-USA/392410356712?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
Once you print just clamp it on, it is self clamping so it might be a little tough at first but it will go on.
I have 3 version that I uploaded so Pick the one you like.
This was printed at 75% infil to give it strength, an at this infil it was a very tight fit.
It has enough strength to hold on.