You would need them pretty closely spaced, and they may interfere with the prop in turns, but it would be doing a similar job to internals, albeit with a lot more welding on the outside ones.
Indeed. I would think I could stitch weld them though, as long as the hull is sealed.
https://www.youtube.com/watch?v=qiYOvTV8Ewc
In the above video is the boat I want to build, or at least similar. You can fast forward to about 3:00 in.