Deja vu all over again. We just had a thread on this in the past week or so.
Easiest thing to do is mount it on the dash, just behind the windshield (inside the car like they tell you NOT to do). It works perfectly fine ~ 95% of the time.
You can either put a little piece of Velcro on it and the dash or, as I did, mount a very small piece of sheet metal* (talking maybe 3/8" x 1") on the dash with PSA and let the magnetic antenna cling to that.
*I'd bought one of those little magnet holders for my cellular phone and this came with a small black piece of metal with PSA on one side. Its purpose was to attach to the back of the cellular phone in case it was not magnetic. Didn't need it for the cell phone but it worked just fine to stabilize my little XM radio puck on the dash of my '84 convertible.