Its a pretty big tank, im not sure you can fit that in a 90cm x 25 cm Dantomkia shaped bot. In fact im pretty sure you cant.

4 mm polypro as a base, you might as well leave it open. You cant bolt anything on it as it warps and flexes all over the place. 4mm hi-grade Aluminum like 7075 or 6061 would be a much better choice.