Hello; Two things. First the welding with the tank in place. To get a good weld a lot of heat is needed in the joint. I do not see much chance of doing so with the tank sitting on the stand. In addition the heat will cause some expansion of the metal at the weld. But if you try it please post the results.
Second thing. The tank is 3/4 inch glass. I have seen pictures of large tanks supported on cinder blocks only on the ends of the tank. In the pictures the tank is supported all around the perimeter edges of the tank bottom. The notion of somehow adding a support touching the glass across the middle raises a question. A truth tho is I have not fooled with a 450 gallon tank so have no actual experience to call upon.
There were in the past some threads about mounting tanks with foam or some other directly under the glass.
Good luck
