A little bit more than a week ago I've deployed empty housing at 60-70ft depth (depending on the tide) and left it there for a week. After taking it back to the surface and inspecting it I discovered it was completely dry inside. I suspect that continuous pressure change may stress out and eventually damage rubber 2'' cap but hopefully it will last for several month before flooding.

After some break I was able to finish mounting PyBoard and battery on a PVC insert that will fit inside the housing.

[It's a piece of PVC I cut from a square PVC post that I had before. I roughly ground it with my dremel tool so it fits snug into 2'' PVC pipe. One thing I should've done differently - mount PyBoard more to the left if you look at the picture - it would give more space to grab when pulling out this insert from the housing. Axes drawn for convenience.]

Reverse side of the insert. Battery 18650 is used. I chose this kind of battery for a few reasons:

• Good enough capacity without the need to assemble several batteries together
• Perfect voltage for PyBoard (3.7v when PyBoard needs 3.3v
• Good fit for the size of the housing
• Available battery holders. (It was quite hard to find holders for AA batteries that would have desired geometry. "Three in a row" would not fit)

Insert half-way in the housing. Had to make cutouts so rubber band that holds battery holder from spinning doesn't get in a way.

The other side of the insert with battery. Battery holder I got has only one hole for a screw and thickness of this PVC insert and type of screws I got didn't let me to fix it well enough so use this band to keep battery holder from spinning around.

Mount loop. It is some nylon rope I found during one of the dives (some crabbers probably lost it). I used stainless steel band clamp to attach the rope to the housing (with a few loops). I've wrapped areas where I expect abrasion with vinyl tape (clamp and part of rope that will be rubbing against rubber cap). Axes showing board orientations were drawn for convenience.