You are wanting to put that tank on wheels? Do you know what the weight capacity of those casters is? Do any of the casters swivel (otherwise you will only be able to go one direction)?
You are wanting to put a 950 gallon tank on wheels, which is going to end up being nearly 10,000lbs. Just to put that into perspective, that is near the same weight as two Suburbans. I really think you should think long and hard about putting wheels on the bottom of this tank.