Hi Rubato and jsharr, your idea sounds sane - thanks. I will look at some sort of turnbuckle looped around the left and right of the cross bar and then to the trailer chain point on the towbar to help keep it straight. Still have to figure out what sort of friction based material to use that is also UV resistant? Since the bar sits on the tow tongue all the time... Ie. I don't remove it. I'll take it to the mechanics and get them to tighten it properly since it's obviously too large for standard hand tools.
ksisler - thanks for the reply - the towbar and tongue are more than capable of taking the weight. I have towed all sorts of things with this setup. It's a very heavy tongue and the only reason it drops down is to lower the height so that the trailer sits a bit lower, because it's an SUV (Mazda Tribute).