It seems to me that the camera, when looking through the curved pexiglass waterproof container, will experience some severe astigmatism (i.e. horizontal and vertical focusing is different).
Fixing this could be as simple as using a cylindrical lens taped to the front of the camera to compensate.
I have used regular convex lenses in the past on the front of webcams to increase the focus distance to infinity (most webcams have limited auto-focus range that doesn't go out beyond six feet or so).
I think that the effect of the 100mm diameter tube is that it acts as a -6 diopter cylindrical lens. Thus we need a +6 CYL, 0 SPH correction lens. Happily this is a stock eyeglass lens, so they are available for a few bucks.