See Gary's website for overall "Buffer" dimentions.
Edit - looks like Gary beat me to it.

Buffer module along will be fine in popular enclosure size of 12X12X4.
You can try something smaller

You might be forced into making a cut out for the tube. Amp is said to run on the cool side but adequate ventilation never hurts.
If you plan to integrate the battery into a single unit, full size would be in order...., something like 19X11X4.
I could be wrong - it wouldn't be the first time.
Nice case will cost you a bit under $100.
You can also get custom wood case made by AC member or "plug & play from Gary.
Mariusz
