Have you looked into the "MirrorTap" solution.
You can get the cable on the "BlendMount" site (which looks to be a great radar detector mounting solution BTW) that lets you tap the electricity right into the review mirror and avoiding running cables anywhere.
I have never done it myself but it looks pretty straightforward and you can select a Chrysler 300 on the website and it brings up a cable that appears to be compatible with that car.
I'm surprised nobody else has mentioned it? It seems like a much more attractive and straightforward solution than running cables to cigarette outlets, et cetera.