30 years ago, I built myself a cabinet for a 125 gallon tank. The base
consisted entirely of good quality pine 2x4s with a 3/4" plywood sheet
topping the base. I then built a floating cabinet without a back out of
veneer quality plywood to encompass the tank and the base. It worked very
well for the entire time I had the fish tank. Never any leaks or swaying or
skewing of any type from the base.

For simple feeding or simple maintenance the cabinet had smaller access
doors on the top. But it was especially handy because I could just slide the
entire construction out from the tank/base for major cleanings or full
maintenance of any type.