So I've researched this to no end and I cant find solid evidence one way or the other. I'm deployed so I cant test it myself but I bought an aftermarket double din radio and SiriusXM receiver and I want to install the antenna inside the cabin. I have seen several different locations but I would like to avoid routing it all over the car to test it if possible. Ill attach 2 pics I've found plus I've also heard of it being on the back deck behind the rear seats too. I'm just seeing where people are getting the best results, Thanks for any input.

 

for best results make sure the antenna has a mostly clear view of the sky. My favorite spot to use is in the dash. Behind the radio cavity there is usually some ac vents or a flat spot big enough to stick the antenna. Just be sure to use the sticky metal base that comes with the antenna.

being mounted under plastic is not an issue, as long as there are no other obstructions, which is why far forward in the dash usually works great