Tai Fu my friend what I do which is pretty easy is to use a combination of methods to make the dish sanding much easier and quicker.
For the back of the rim/guitar the sides are pre-radiused using a method that Colin came up with where the actual radius is transfered from the dish that will be used for the back to the sides. Then the sides are cut out to match. With this method very little time in the dish is required. I can't find a link right now but will keep looking and post it when I find it.
For the top/front of the rim I shim the neck and tail blocks so that all that material does not need to be removed in the dish. Here is a link to how I do this: http://luthiersforum.3element.com/forum/forum_posts.asp?TID=9528&%20amp;KW=(pics)#forumTop%22
I like to keep the top side of the sides flat when bending and when gluing in the blocks so I can do it upside down, the rim not me......
, on a flat surface.And it is helpful too to radius the rim, front and back, in the dishes prior to gluing in the kerfed linings. It's just a lot less material to have to sand through and then the linings can be added, 1/32 - 1/16th" proud and sanded in the dish to form the radius on them too.
Lastly I like 80 grit paper in the dish - things move along faster.
I hope something here helps.