Filling our electronics chamber with mineral oil (or some other non-conductive fluid-- liquid compensation) has certainly been considered. The issue with doing that with this specific design is that it is built to be neutrally buoyant(ish) with the chamber filled with air. If we filled the Electronics Tube with mineral oil, it would be considerably heavier and a lot of additional flotation would be needed to keep the ROV from sinking. Additionally, we'd have to figure out a way to focus the camera (since it would not have an air-glass index of refraction difference any longer and the air gap in the lens system it comes with probably wouldn't handle much pressure). We would also likely encounter issues with the brushed DC motor in the tilt servo. Finally, filling the Electronics Tube with mineral oil would make everything a lot more messy to tinker with, which at this phase we do a lot.
That being said, liquid compensation would certainly improve the depth capability of the tube as well help with heating issues. If you (or anyone else) wants to experiment with it, it would be really awesome to see what comes of it!
Right now, I'm working on a modified endcap design that would incorporate a thicker o-ring that may hold a better seal even with the wide tolerance bands of the tubes (which ultimately is why we have trouble sealing a lot of the time). I'll be sure to post how that endeavor works out, and please keep us posted on any other thoughts you have for leak prevention as well.
Thanks for the idea!