Dale - I do not know about your reloading bench, but I would have a hard time getting that thing on mine.
A little more seriously; the design you are talking about is huge, it would take a lot of media, be very difficult separating the brass and media (you need to dump it some how) or scoop it out (slow), takes up a lot of space. Unless you are going to "tumble" large amounts of brass, the brass is going to be hard to find in the media, when you try to separate it. You could make a large screen for it, but that takes up a lot of room and more work/expense. I do not run any wheres near that much brass at a time. I have found that I can not run two very different cases at the same time. 22 hornet and 44 mag brass will not be friendly in a tumbler, believe me. I try to run mine in lot batches of 50 or 100 at a time. I have set amounts for each lot and do not separate them. Seriously, I find this very impractical on many levels. I think that the few bucks you save would be money well spent on a ready made tumbler. Of course you have the pride of doing it your self, but I think you will find it quickly gone when you try to use it. If you decide to go ahead with this project, I predict you will soon abandon it and go buy one any way
just my 2 cents