I keep getting water into the EVSE which causes all sorts of problems. Is there a particular trick to waterproofing the unit? Is it possible I am missing a "seal" around the front portion of the box?
The enclosure seal looks okay. see notes on your image.
The most common area for leaks is the display seal under the clear LCD window/brace, screw seals and the button.
Ensure the rectangular seal in between the enclosure and window.
Ensure there is a seal under each of the 4 screws on the outside.
Ensure there is a between the button flange and enclosure on outside.
If you continue to have issues with the display and button seals you may want to consider WiFi instead of a button and our newer clear enclosure which has 0 penetrations/seals for the display/button vs 6.