I suspect that Paul is right on target...a cylinder type WTC will probably end up being the most simple, reliable way to go. The trap that you want to avoid is like the old tale of asking a guy the time, and he tells you how to build a watch. Keep it simple and workable. Since this is your first sub, there will be lots of challenges just getting the thing to run and dive. No sense in getting so exotic that the whole thing just gets to be more trouble than it's worth.
You can build your own Lexan WTC with a couple of endcaps annd seals from a place like Mikes Subworks, and tubes and parts from McMaster-Carr. You will have lots of ways to use your creative talents in a very productive way as you build your boat.
"The Japanese solders would die for the Emperor, which made them formidable. The U.S. Marines would die for each other, which made them invinceable"...Iwo Jima