from an engineering point of view, that stand is designed to bear the load of a 180 gallon tank on the perimeter where all the supports are. if you decide to put a tank that doesnt exactly match that footprint, there will be stress risers where there is no supports. even though there is a piece of wood covering the entire stand, i doubt that it will be able to distribute the weight of the tank away from the middle and out to the corners without failure. if you think that wood can support the weight of the tank, than by all means try it, but i think that the wood rather than the stand is going to be taking the brunt of the load, which is far from optimal.