Thank you for you concerns. I appreciate the feedback and advice.
As you can see in the following pictures we started with the base of the stand, attaching 2x12's to the 6x6's. Flipped it over (already getting heavy) attached the wheels and installed bolts by each wheel (just to be on the safe side). Put it down on the wheels and continued installing 2x12s across the top of the 6x6's. This will insure that the plywood bottom of the tank is fully supported through out.
As you can see in the following pictures we started with the base of the stand, attaching 2x12's to the 6x6's. Flipped it over (already getting heavy) attached the wheels and installed bolts by each wheel (just to be on the safe side). Put it down on the wheels and continued installing 2x12s across the top of the 6x6's. This will insure that the plywood bottom of the tank is fully supported through out.