We receive many inquires where one wants to coat plywood tanks. I suggest that we quote you a 1 gallon pail of our Pond Coat delivered. (Please email us your address.) Please try it out to make sure that it will work with the Marine Plywood and Acrylic. Apply the product in thin layers until you reach a 50-60 dry mil membrane. Make sure that you avoid puddling in the corners. Furthermore, before filling the tank with water you will need to make sure the membrane is completely cured. The cured membrane needs to be 15% or less moisture content. Home Depot sells moisture meters between $7-$15 dollars. To cover 300 square feet you will need to purchase around 15 gallons of material to build a 50 mil membrane once you decide this will work for you.