I cast a block then turn it down, that way I can custom fit them to the tube - it takes about 2 hours to cast & turn 4 caps.
Yeh, it's a big boom box, but that is the WTC from my Alpha, the Vanguard one is abot 550mm long, I've got capacity for 1.5ltrs water. I've weighed the top & the fittings, I need about 1kg to dive her, so, allowing for air storage, I should be ok.