Hi there,
I'm a long way from Alabama but I thought I would chime in, if its ok.
I wouls seriously consider waterproofing that wooden floor, even if its a clear layer of adhesive plastic over the top.
I cannot belive this wasn't recommended before you started the project.
It does not matter how careful you are, the surrounds of the tank will be exposed to, and absorb the moisture.
You do not want the timber warping or swelling over time, and unless you act now, it will definately occur.
I have seen this over the years, time and time again.
Good luck! Seems like a great project.