i have a '70 Kombi which when driving at speeds above 50 or with ever so
medium cross winds or any winds at all for that matter, does the same thing.
i have a friend that has a '69 kombi that he drilled holes right through the
top of his bus just forward ov the roof cut-out, and put really long carriage
bolts and washers through it with wing nuts on the ends so that he could
still open the top. while this is not exactly stock engineering, it did work.
i am not too crazy about drilling the holes though so if you get any other
way of remeding the situation, i would like to know. :{) peace.

                                       "Going where the wind don't blow so
strange"