walthers has over 900 display cases for trains and the likes, here is one example for G scale, they are 6" wide/9" high on oak and can be had in dozens of lengths...It looks small but that train is huge. A 24" case would look natural for a bb...
http://www.walthers.com/exec/productinfo/248-2436
Just do an advanced search for display cases in G scale they have about 15 sizes in three different wood colors. The ho/o cases can fit many smaller 700/500th kits and they have HUNDREDS of them. A 24" wood G-scale one is about 120 bucks. In G alone they have 6w/9l in 14/20/24/28/30/32/36/46/and even 60"! It would be cheap to do a longer case and put three or more destroyers in one case on a shelf or mantle..I plan on doing that with a sprucan/burke/ticon all in one box down the breakfast bar.

If you use brass doorknobs you can probably tack glue them to the case with a little rtv or double sided foam tape and remove/replace them at will, so a 'better' model can take its place later and the holes don't need to match. in the base. Something like an Iowa wwII/modern then/now two ship display would be cool. I'm really thinking about a 46" case and I can just rotate the models in there as they get better.
I have never called walthers to see if they have G scale grooves in the wood though. I probably wouldn't care either way.