If your housing has a space reserved for flash trigger. It can be used to install a lithium polymer battery. It's a rudimentary method, but it works and will last for a day's diving. No need to open the housing.
battery are cheap and can be recharged over and over again .
I have an A7R2, nauticam housing.
28-60+WWL or 8-15+kenko+metabones, which is a better choice?
I usually travel in the tropics to dive. shooting sharks, manta, turtles, etc...
Looking forward to your suggestions.