What are you trying to do/achieve? Most lights will reflect badly off the glass. What size unit are you thinking of? And as someone else said, what vehicle.
If it will be pulling a lot of amps, it'll need wiring to correctly support it. Which in most cases might just be easier to run a live down the vehicle to it. But it really depends, I suspect pulling a Disco 3/4 apart to run a wire under the carpets would be a ballache. On a Disco 1, not so much.