It certainly can be figure out mathmatically, probably to about 10 decimal places but it won't mean much. The angle on the front of your trailer is relatively small meaning a direct horizontal wind force will impact very little of its force downward, most will be backwards... :-( As the previous poster indicated, the downward force will be counter by a "lack of force" over the lead edge of the roof... just like a aircraft wing... resulting in some lift. Hence, the difference will be minimal but certainly a good exercise for some engineering student to get bonus marks in a dynamics course.