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Nice job. Only one thing to think about. That tube mic that you are using does pick up a lot of surrounding noise. I think that I would have made the box bigger. The other aspect of a bigger box is that you will not feel like you are so enclosed in such a small space.
You are probably getting this question a lot. What is saddle stitching technique? I have some leather that I wish to make a sporran with, but I am unsure of how to hand stitch it. Maybe this will help me with my project.
If you ever do need to use the bilge pumps, as it is, you may have a vacuum problem. In order for bilge pumps to actually work, you need to have a vent for air to replace the water, as the water is pumped out. Not much is needed as air will travel faster thru a vent than water will. You can use small diameter pvc pipe, and have it curled over to protect it from any waves, rain, etc. You can also use an end cap that can be removed as needed.