Just got an update from the machine shop. He’ll use polyethylene.
Another improvement is to make the 3/16” o-ring a little snug so the lid wouldn’t get easily loosened by a bump. With the clear wall you can really see the sealing face by the width of the flat part of the o-ring. That’s the reason I pick thick o-ring (3/16”).
Also there is an option to add 2nd sealing surface, if needed. That is the 2.5” ID x 3” OD x 1/16” thick gasket underneath the lid flange face, as shown in the drawing. That gasket can also act as another restriction for the lid from getting twisted open by accident. To prevent such situation to occur, basically you have to twist the lid hard enough to open it.
My prototype PLB case would cost $125 (1 hour labor of $90/hr + $35 of the material). As you see in my earlier post that just the 2.5” ID x 3.0” OD acrylic tube cost $65/ft. It will get cheaper if we make more.
It’ll be finished in 2 weeks. Then I’ll test it later in June when I go diving in Flower Garden Banks. So, stay tune!