A great sanding bar can be made from a Belt Sander belt and a 1x4 board. Get a belt and cut it across the splice. Use some carpet tape and tape the stretched out belt to the board. Use a fairly course belt, IE 120 or so. If you would like a finer mesh, you can put it on the reverse side. You can get belts to a very long length, but one that opens to about 24" is usually all you will need. The long length prevents you from rolling the edges much as a 1" stroke will sand the whole length of an aileron on most planes.

Don