I think I did say "at a minimum". It would also depend on what you coated the greenboard with.
When designing my fish room I had the luxury from starting from scratch as we were building an addition. I had my architect deisign what he thought would be needed and given that he has designed many homes with indoor swimming pools, I think he had some experience here. I then added to it.
My room is 100% greenboard (which raised a few inspectors eyebrows) and coated with some sort of elastomeric paint and polyuerothane (3 coats if I remember), gave the painters fits being in that little room with those fumes. The floor is tiled with a drain in the middle. There is a 250 cfm commercial rated bathroom exhaust fan wired to a combination thermastat/dehumidistat that turns the exhust fan on if the temp or humidity rise above a number that I am able to set. I also have a separate AC unit just for the fish room rated at about 3-5 times the square footage.
AND the kicker, living in the desert helps a little with average humidity around 10%. It was kind of funny when my wife walked into that room and asked me why the walls were so shiny.
The results have been that there is no noticeable himidity difference in that room, no mold noticed at any of my monthly inspections (kind of paranoid about that), and no need for a chiller on my system. The average temp in the room is 75 degrees and the tank temp stays between 79 and 81. If my room AC goes out, all I will have to do is open the front access doors or the door to the room and put a fan in there to get air from the main room. It has it's own system as well. The make-up air (due to the exhaust fan) that feeds the room when the exhaust fan is running comes from the main room which is also kept around 73 degrees, 70 in the winter.
The tank has been up for about 14 months now and no problems related to temp or humidity so far, knock on wood.
It will be very interesting to hear how those gaskets end up working out and if your tank runs hot. All that exposed wood would just make me worry, gaskets or no gaskets.
Good luck with the project and keep us posted. It still might be a good idea to add an exhaust fan on a dehumidistat, IMO.