I generally pot the OpenCTD with E-90FL epoxy, but because there are some fiddly bits around the pressure sensor, that component is usually potted separately, first, with various flavor of fast set epoxy. That secondary potting has been a failure point for several CTDs, and E-90FL is not always easy to find, so I've been experimenting other possible epoxies. 

JB Weld MarineWeld is appealing because it's pretty inexpensive, easy to find, and easy to work with. Unfortunately, it turns out that it's just too viscous to e reach all the voids I need it to. 

I did a test potting this week to see if MarineWeld could work in a pinch, but, as you can see, it left several voids under the pressure sensor that could contact seawater. 

And when we cut it open, it leaves a huge void around the sensor. Glad we sacrificed this one to get a look at the inside.