I have been working on the water tight cylinder (WTC) design to protect the electronics from the sea water. Right now I am using a 3D printer to prototype different designs but will probably machine the final parts from a solid block of plastic with a 3-axis cnc milling machine.
Over the last four nights, the design has evolved into a set of caps with the top cap having a built in handle. By pulling on the handle, the entire PCB assembly is pulled out of the cylinder for maintenance and repairs and to retrieve the SD card. The final design for the end caps will have two large grooves for o-rings to create a water tight seal between the cap and inner wall of the WTC. Alternative ideas (I have not printed these yet) include a bulk head and flange assembly that uses cap screw to clamp the end caps onto the pipe.
The designs shown in in this post are part of a design where the end caps have a twist locking feature. At first, I had planned to have this assemble completed sealed inside the WTC but now I am considering ways to implement this design but also have the twist-locking feature be the actual cap. This would allow for a permanent and secure connection point for the GSM antenna which could then be potted with epoxy to ensure it will be water tight while also preventing corrosion and damage.
One concern with potting the connection, however, is the possibility of crevice corrosion of the potting material is not properly applied. This could create very small crevices and gaps between the metal antenna connection and the potting material and result in dangerously corrosive micro-areas that result in excessive corrosive areas.