You only want to have to do it once so I'd avoid MDF if it were me. If you want that gloss piano finish like CADlights stands have then you are looking for formica in gloss white. I'd use 3/4" plywood then contact cement the formica to the plywood. Over cut the formica then trim flush with a router. If you want it real clean counter sink some coated rare earth magnets before you cement the formica on the back side of the panels. Then you can fully remove all panels for max access under the tank.
You can have the lumber yard/ or HD/ Lowes cut the plywood for you. Then all you need is the router and two bits, and a heavy roller to do the rest yourself. There is a formica wholesale that sells to the public in Cypress, I believe a 8x10 sheet of gloss white was around $58 bucks last time I bought it.
Don't get the low VOC contact, get the original formula (red label) in the quart or larger you'll go through more than you think.
