I've heard that you should put a fairly large capacitor (not something huge for car audio) on the back up wire going to the relays. That makes it take a fraction of a second before the relays engage which prevents the HIDs from turning on when you're just shifting from park to drive.
I put some cheap driving lights on my truck mounted under the rear bumper. Those are nice because I've aimed them so they light things up about 30-40yds back. I doubt (but I could be wrong) that your H.I.Ds light up that far. But what they do light up is nice and bright.
If I had the funds to I would put some HIDs in my rear driving lights and maybe in my tails like you did. That would give me a super bright light field all the way from 0-45yds from the tail gate