I am building a K-350 and am trying to figure out how many cubic feet of 02 I will need to have on board to support 2 people for 72 hours. My hull ID is 36" and I am using a length of 7.5 feet long to include the end caps.The conning tower is 23" ID X 18" to include the hatch. I came up with 57.32 cu ft. Is this correct and if so, can someone tell me how many cu ft of 02 I would need to carry based on the average aspiration rate of two people?ThanksRick P.