Is this stand ok for the 75 gallon?

So I bought this tank and stand off facebook market place. It was used as a reptile enclosure it appears but the guy who sold it to me said it held water fine for a month. I am mostly concerned with the top of it being open. I have filled it about 80% of the way and so far so good. Just wondering if the edge will be strong enough to support it. Does a piece of ply wood make that big of a difference?