Something also came to mind. I had a look inside my Line 6, and it made me think. The amp itself, is quite small, and would more than likely fit into a re-engineered box. Or event just a small wooden 'shoe' as the amp comes out with the face plate intact, so you would still have all buttons and printed plate in place.
The box, then, since is blanked off inside could be made smaller? I'm not sure about this, but I'm sure Alex from Bare Faced might be able to help you. If it did work, you should get two very small component parts with a goodly amount of oomph! PLus if the amp is in a back pack then it would be less likely to get weather damage, whereas the box, if needed could be replaced at a much smaller cost.
This is strictly theoretical as I have no idea about building cabs. But if the box is the same size, then why not.....no?
I know im going to start a debate about cab design now!