I know I am a little slow with this post, but I use all three, DC8, DC4HD and X10 modules. It seems to me that I have more reliability with the DCs than the X10s. The most noticeable difference is with some of the electronic ballast.
As for the electrical, if you go to an electrical supply store, they do have a silicone like substance that they use to fill underground electrical boxes with; like boxes for underground lights that would shine up on an office building or what ever.
I have not decided for sure how I will do my electrical yet, but I will not use metal boxes. I will use either the fiber glass or the plastic. I like the fiber glass better. Your fish room is well ventilated and climate controlled, I donââ"šÂ¬Ã¢"žÂ¢t think you will have that much problem with condensation in the boxes. Your boxes are mounted straight up and down so even if there is some condensation, it will not be dripping into the outlet. And as suggested previously, if you are concerned, you can wrap the outlet terminals a few times with electrical tape.
I really appreciated the ventilation thread. I got some good ideas form it.