I build custom Casings or WTCs ,very strong 1/4 in walls sealed with a special radial seal .One trist and it opens.
Your choice of ballast systems or the one I recomend ,the non pressurized ballast tank pump system,scale dive and surface and hovering,no need to add or remove wigthts at different lakes and completly safe and Eco freindly.
The Casing has 2 removeable caps and random acsses along the Casing.
Engineered not to leak iether from the out side or from within and made from the same material that Scuba Camarra Housings are made from.
No stress desighn in the equipment tray and standard servos are used along with bellow seals that will not jam or leak over a long period of time.
Stainless Steel shafts and oilite buchings packed with grease make the stuffing box.
Water cooled geared drive system for single drive or dual drive or not.
4 inch OD 3 in ID.
For more info see: The Affordable Expandable Casing in this same topic.
Here are some examples
PM if inteested