Some bikes are most definitely more susceptible to buffetting wind more than others. Depending upon the bike, adding a windshield, particularly a fork mounted windshield, isn't really going to help the problem.
On the other hand, I've noticed that different people on the same bike seem to be much more suscpetible to cross winds than others. For most people, this is a result of maintaining a tight grip on the handlebars, frequently made worse by the anziety of riding in windy conditions. When you have a white knuckle grip on the bars, every movement of your head or body transfers to the bars and causes the bike to steer. This sets up a vicious cycle wherein the rider tightens his grip even further, making the next gust even worse. I ride the Bay bridge quite frankly (although never on a Marauder or even a similar bike). On my various bikes, I've never felt buffetting that upset the bike much at all, unless weather conditions were really ugly (stormy).
Before you spend a bunch of money and time on a project which may or may not help the problem, I would suggest that the next time you ride over the Bay Bridge when traffic isn't too bad (yeah, that'll happen!), try relaxing your grip on the bars as much as possible. I find it a useful tip to tell people to flap their elbows. If your arms are relaxed enough to flap your elbows, they are usually relaxed enough to damp all but the strongest inputs from wind.
I suspect that you'll find that the wind effect is greatly reduced when you are relaxed. Once you see it for yourself, it usually doesn't take long for you to learn not to tense up in adverse conditions, instinctively. This GREATLY increases your chance of a positive outcome in all sorts of potential incidents that can occur on a bike.
If that doesn't do it, I would try to find a Marauder riders group somewhere on line. Every bike reacts to a windshield so differently, and most bikes react to different windshields in very different ways, that it is worth consulting the collective wisdom of a group of Marauder riders, who will be able to direct you away from shields that have proven to be troublesome.