You can make anything waterproof by dropping it in a ziplock bag
You can also make anything waterproof by using silicone caulk, provided you don't intend to open it ever again. In the case of the e-LVT, you need to access the battery, the side connectors, the 510 connector, the buttons... I suppose it could be done, but not easily, and probably with mixed results.
At any rate, the stock
device is as waterproof - or water-resistant - as the Titanic.