I would build a dedicated support frame using 2×4 stud material in the same dimensions as the published base. A single 4 foot 2×4 can support over a ton of weight, so no need for overkill. Then build the top section and skin out a frame around the tank.
Otherwise, just build the published design and beef up the center support with 2×4’s that carry the load all the way to the floor.
30 gallons is only about 30 gal * 8.33lb/gal = 249.9 lbs