That's a really neat kit, Izzy. Thank you for sharing the image. I believe that's the way to go with the PSK.

I'm using these in my BOB and Car kit. Tested it in salt water several times swimming and snorkeling. Works very well and is in perfect shape still after about 7 years of infrequent repacking.

I have these too (have repacked the DR PSK with one). They are holding water pretty well even when snorkeling down to 30 feet, however the plastic is probably not UV resistant (or perhaps it's just deteriorating quickly). The seams on oldest of mine became brittle and developed cracks after just a year or so while simply sitting in the pocket of my GHB.

Did you noticed the automatic air purging valve on the side of this box? It's there to compensate for the air pressure change as your altitude is changing. So if for example you are traversing a steep downgrade of a river and found yourself in the water while continuing to descend rapidly, it will suck water in automatically as the air pressure outside is rising.

There are plenty of dedicated containers available for scuba divers. If improvising, I would get a rigid metal screw top capsule, wrap it with a piece of innertube (to soften the capsule's edges) and put it into an abovementioned aquapac bag releasing as much air as possible. (I think a thick freezer bag will do OK too if you wrap it tight at the closure in a similar way, securing with rubber band from unfolding). The capsule will prevent its content from crushing under pressure, the bag - will waterproof it creating the double seal. Even though the aquapac bag may be rated for 30 ft only, I don't see why it would leak at 150 ft deep, provided the capsule can't puncture it. At least I had my point and shoot camera in such a bag (rated for 30 feet) at 80 feet deep without a problem (the cmera stopped working as all of the buttons were jammed under the pressure, but no leaking or bag damage noticed).

All the complexity (and price) of typical underwater containers is coming from the easy frequent opening and closing requirement. The PSK is a single use item. One can consider a permanent gluing/caulking of the seam/thread of a rigid enough container. Just break it in an emergency.

Agreed - around water -- or even everyday -- a plastic container is often better. I'm experimenting with "lock lock" tupperware style boxes.