Enclosures
Main Electronics Enclosure
The main enclosure is by far the most complicated (and expensive) part of the entire submarine. Because of the tolerances needed on the seals and bulkhead penetrators this was not something I was able to manufacture myself. That's not to say that you couldn't. I've seen lots of impressive builds using PVC and acrylic windows but most of those designs were not likely going to withstand the depths I was hoping to reach.
Although you can really build the enclosure out of just about anything that is designed for the pressure, you'll still need a way to get wires through some kind of bulkhead. Some kind of "penetrator" will be needed to create a water-tight seal between the bulkhead and the wire.
I'm using these WetLink Penetrators: WetLink Compression Gland Penetrator for Subsea Electrical Cables (bluerobotics.com)
Battery Enclosure
I created the main part of the battery enclosure out of 3in PVC, and a pressure rated end cap. On the open end I used a 3in flange and bulkhead plate from Blue Robotics. So far this is working very well, without any leaks. However, it's a bit of a pain to get the battery in and out. It takes 6 screws to secure the end cap and that takes time and each time I feel like I'm going to lose the screws. This is a difficult engineering problem to create a water-tight seal that is quick to open and can be used many times without the risk of developing a leak. Blue Robotics is working on a new version of their 3in enclosure which may solve this problem, but I have not seen it yet.