some friends of mine were big off-roaders with huge light bars. theirs were all home-brews. if you've got roof racks, a two-by-four with some clamps will let you strap it down. I found that when I stopped requiring logos and pretty details on my gear, I could improvise just about anything with some two-by stock and some form of clamp/bungee cord. Or make friends with a welder and let them build something for you.