I do my final sanding by hand but with a twist.. I take foam, like the stuff Dubro sells for wrapping your receiver or putting under the tank.. I cut that into 4"x4" pad and use double face tape to secure my sandpaper. It gives you something to hold on to and doesn't allow the paper to get any bends. The bends are what will gouge the balsa and the foam allows it to go around curves real well.. A bar sander for final will give you flat spots real easy.. There are many ways to do your final, this is just how I do mine.. Love to here how others do it... One thing though, i don't do my final till I am ready to glass or cover.. Just working on it in the shop you get more dings... Man I wish I was ready for final sanding...
Jimbo