While I agree that the Boost adapter does provide water resistance, I always like to have the option of not having to buy something else (in addition to the fact that you lose some adjustment ability with the Boost). This is a solution that we have used for years on GoPro cameras. But it works on the Mevo as well. I realize this is sort of a "farm engineered" solution...but I was raised on a farm. Basically stretching a zip top bag (with a starter hole) over the camera creates a seal, and a drape that covers the lower portion of the camera; namely the USB port which is exposed without the Boost. I generally keep rubber bands in the camera bag, but living in a house with ladies means there is also a fresh supply of hair ties. They work as well to better seal the opening around the camera.
Here's a 4 year younger version of me walking through the process on the GoPro: