I would think that's pretty self explanatory for a number of the reasons already listed for the over head.
1.) it doesn't get much more visible than on the front dash.
2.) any hard off-roading and it's hitting you in the teeth instead of the top of your head. Or it flies up and cracks your windshield
3.) sun damage... I don't care what type of rifle you got, storing long term in direct sunlight is never a good idea. Will it affect the operation if the weapon? Probably not, but when one side of your little black rifle is light gray your nit going to be happy. Even worse if you have a wood stock.
I've been brain storming for a good year on how to quick mount my fun guns in the Raptor. I've got a couple of ideas, but I just haven't had the time to draw them up and give it a try. Hopefully things slow down in the next couple weeks and I can give them a try.