I deployed several sensor stations in a coastal estuary with brackish water in southern Delaware about 5 years ago. There’s no difference between those stations and any of the ones we put in fresh water except that we used titanium-body turbidity sensors instead of stainless steel. The other sensors were all rated for salt water use, and I used marine science installation techniques for everything else we did with those stations. These are the same techniques you’d need to use no matter what type of logger you want to use. There are plenty of resources online about how to install monitoring equipment in marine environments, and you can check with the manufacturers of the sensors you want to use to see if they recommend using their sensors in salt water.