Should be neat. I defiantly agree with Danny though about putting an upright brace or two in the center. If you do multiple tanks on top that fill the whole 10ft length then you will be over 700 gallons which will be close to 6,000 lbs. That's like putting a full size suburban on those top lengthwise 12" wood span. 12" wood boards are strong, but it does lose a lot of strength when it spans a distance without support.