Framing was used inside to strengthen the CT area. The hatch was constructed of 0.25 inch steel and has a 20 inch opening. The hatch has double seals made of neoprene rubber. Most submersibles are constructed with a massive weight near the keel, such a large weight that the sub has little choice but to ride level with only a few degrees of pitch possible if any. Often times the dive planes do not really tilt the sub forward but simply push the boat downward.
Dive planes are totally useless unless the sub has enough forward speed to create the force.
Some subs do not use dive planes but adjust the onboard ballast so as to make the sub slightly positive or slightly negative in buoyancy. This allows the operator to move up and down by allowing water into a tank or pumping the water out with a pump. Adjustments are slow and not the best approach for a fast moving boat. My design uses no changing ballast or dive planes to obtain vertical position. Rather a 325 pound weight located below the hull and above the keel is used to give the sub a 20 degree nose up or 20 degree nose down angle.