One of the most critical aspects of a properly functioning ROV is keeping a dry electronics housing. We've been using the double o-ring strategy with laser cut acrylic end caps and an extruded acrylic cylinder. The tolerances of the extruded tubes and any slight variations in a laser cutter can put the electronics housing at a higher risk of failure.
I've added some ways to test and troubleshoot potential problems with the electronics housing on the Wiki. Let me know what you think!
Also, I think it's a good idea to have tests for every section of the build so that potential problems can be caught early, before they're permanent. More on this soon...