This works (at least when modifying it thriugh the layout designer) : maybe a Refresh() is missing somewhere
Normaly the updateSizes() method recalculates all the internal sizes taking into account the margins but it is for internal use and is called by Refresh()
Question : When you resize you're app, all is recalculated so the new margin values should be taken into account : does this work for you ?

	gantt.SetTopMargin(1).SetLeftMargin(1).SetBottomMargin(1).SetRightMargin(1);

This work in progress, it is mearly at start point : I intend to use it to enable things like selection (draw the point with a different style : highlight for example)