Well, as luck would have it, the flow sensor project went on hold for most of 2012, as I had become the lead illustrator for a very cool book project, and we had recently purchased a circa 1890 Sears kit home, that was desperately in need of some tlc. But in between ripping all the original wood siding off the house, repairing the windows, painting, or laying in a new patio, I was still reading as much as I could about the Arduinos, and learning quite a bit from books like Arduino Projects to Save the World which showed me all sorts of tricks I could use with real time clocks, eeprom memory, bare bones Arduino clones, etc. I went to a couple of Maker Faires to meet new people, started keeping an eye on kickstarters, and finally began to understand why my brother had been going on about how cool the open source movement was for all these years.
So at the start of 2013, I had a 500 pound gorilla in the room: No matter what I did on the electronics side of things, I still had to come up with something that was going to protect those circuits at depth for a really long time. While it doesn’t look like much summarized here, this background research actually took quite a while ( I have hundreds of links in a Google doc somewhere…), so I am posting the highlights here in the hopes that it might help someone else save a bit of time.
My first thought was to take an enclosure that was already water proof, like an otter box or a pelican case, and just stick a few cable glands on it. I had often stumbled across projects like this in the cave diver forums, where someone always seemed to be building their own lights. I even bought a few cases to try it out, but for the most part, I really didn’t think I could trust those feeble O-rings for the job. On top of that those cases were oddly shaped, and I did not want to use something that presented dramatically different cross sectional area with different orientations relative to the water flow.
And then I found several people building underwater video camera housings. These guys were getting serious! Perhaps the best one out there is the one by Bobby_M on the instructables site. But there were plenty of others of the same caliber and untold thousands of other designs to burn away the hours on YouTube. For the most part though, these guys were building really big units, with budgets for the housing alone that went over the target for my whole project. But I still picked up a few handy sources for critical parts, like latch clamps & O-rings.
But the high point of my underwater housing research was the discovery of the home built R.O.V. crowd. Yep, you too can build your own undersea robot. If there is a way to build something that goes below sea level, you can bet that these guys have tried it out. I learned quite a bit reading through their design blogs, especially about things like potting your electronics in wax (which I still have yet to do) and tricks like using bolts, rather than expensive clamps, to seal the ends with home made bell joint leak clamps.
However, after all of that, I ended up back to where I started. You see back when my wife was a starving grad student, we really didn’t have two nickles to rub together. So most of our kit was cobbled together from old equipment other people donated to us (and to whom we are forever grateful). So we ended up cave diving with huge old canister lights, powered by lead acid motorcycle 
batteries, and not a few of those were home made because that’s just how things were done in the early days. But the thing is, by the time we got them, those housings had already survived years of abuse, proving their worth. So I set off again rooting through the archives, for the “really old” dive light builder threads, which in the end, turned out to be GOLDMINES of information. These guys were starting with cheap PVC piping, heat gunning them into workable hunks of flat-stock, and some even figured out how to lathe end caps using only a hand drill and a chisel. After seeing all that, and the straightforward simplicity of the construction, I was pretty much set on using PVC pipe as the building material for my housing, rather than expensive rods made of nylon, or ABS.
Underwater Arduino Data Loggers 