After letting my Maglite roll all over the cab for so long I finally got sick of it. Swung by Cabela's and picked up a couple QuickFists and starting looking around for a good mounting point. Behind the driver's seat on xtracabs there are actually 2 small holes, perfectly placed, already in the metal that are easy to access from the jack compartment. He's a couple pictures with them mounted.
Really easy. All you have to do is poke a couple holes in the carpet. Thought I'd share.