FYI: Water weighs 8.34 pounds per gallon. 300 gal would therefore be 2,502 pounds, or a ton & quarter. That is not counting the weight of the tank, canopy, lights and whatever other accessories you have in mind. The weight must be distributed evenly, (tank level, etc.) or you may end up with far more than 130 pounds in a single square foot area.
This is not to imply that a cabinet maker is not qualified to do this, but one must be aware of the particular challenges of trying to contain H2O.
Just my 2 cents!