I, too, just took the original mounting bracket and mounted it horizontally on a piece of angle iron. I drilled a hole in the chassis near the tip of the antenna, and did some sort of half-assed thing, but it works and isn't coming out. As far as not securing the tip, I think the antenna will want to wiggle back out and "smack" against the fender everytime you hit a bump, but I don't know. I just took the extra precaution and secured the tip.
86 GT -- All Options except Performance Sound