While generally not recommended, you can install the Sensar antenna sideways, however, you would need to provide some kind of air dam in front of antenna when laying down to prevent damage while cruising down the road as well as tree limbs and other obstructions that might grab the antenna and tear it up.
I would suggest that you are better off moving over a bit (I would call the manufacturer and ask exact where to place it) and you will be able to use the same coax from the roof (you don't need any different 12V than you have now) if you have verified that there is strong 12+V power in the coax itself.
