Looking at getting a sleeve for when I put my iphone 5 in a bag or when I have it in my car (I set it in a tray on the dash when it's plugged into my stereo). I'm torn between either a Colcasac or any of the felt sleeves from Etsy. My biggest concern about the Colcasac is whether or not I'll run into overheating issues from using/charging the phone when it's in the sac. Anyone know if this will be an issue?