Watertight Enclosure

I’m planning to build something similar to the original openrov but using Ardusub and a Pixhawk flight control paired with a raspberry pi.

I’ve got most of the parts I need except for a good watertight enclosure. Blue Robotics makes some sweet enclosures but they cost several hundred dollars and I just can’t justify that.

How does the enclosure work on the original openrov? Looks like a cast acrylic tube and some sort of end caps with a oring seal? Any insight or pics would be helpful.