Just get a marine cable cover like one of these, aiming the opening to the bottom. Put a small bead of silicone on the top and side edges and in the screwholes before final assembly.
http://www.amazon.com/dp/B002PI0R8K/ref=cm_sw_r_cp_apa_i_cIniDbC8CE6Y2
There are also stainless steel versions that may have a bigger opening for those larger wires.
http://www.amazon.com/dp/B07MN26G9S/ref=cm_sw_r_cp_apa_i_kLniDbQYRE154
Otherwise a small tube of black silicone would work just fine, just make sure you get all the way around each wire, and let it cure fully before use.