I missed how big is the box, and would it be permissible to
splice the wires rather than use a coupler.
I read years ago, when I tried -- (and things change) that I
could not buy a coupler rated for this in a DRY location.
This is switching from an electrical problem to a plumbing one.
While
You could use two of these:
http://www.alliedelec.com/search/productdetail.aspx?SKU=556amp;R=500-0056amp;sid=456F70806D65617Fhttp://www.alliedelec.com/search/productdetail.aspx?SKU=556R=500-0056sid=456F70806D65617F
