O.K. posted question taken seriously : I had to install many of those aftermarket chrome hi/low/off deals in the dump trucks I repaired for a living . ME ? on our Dodges with the doubble steel roof ? I'd use short fat ( # 10 or 8's) sheetmetal screws and put it somewhere on the passenger side of the rear view mirror .... no matter where you put one , dash or ceiling , it blocks your view somewhat . It would stay up there as long as the screws were drilled properly and tight , but if OFF roading , eh may the dash is better with a backer "washer"* underneeth the plastic ? makes cleaning windsheild a PITA ...
* a 4"x4" piece of tin that the machine screws / nuts can bolt thru ,