I would go with a stopped T&G, that way anything that gets exposed either way will be a square edge. You can allow plenty of movement room on the ends without it showing. Drill your pins, remove the BB end and elongate all but the center one or two holes, 1/4" each way. With a T&G you can make a deeper groove and tenon than you can with most dovetail bits, which will add great stability for the BB ends from tipping down. The tongue/tenon can fit tight in thickness. After all, you can't make that sliding dovetail tight or you'll never get it together unless you taper it, absolutely perfectly. Absolutely perfect and woodworking don't often go together so I avoid that challenge, there's no money in it, just heartache. Which is where I think you are headed with a sliding DT BB end.
Last edited by Hammer1; 08-21-2011 at 10:39 PM.