I used deck screws. No problem. I used blocks with wood glue, pin nails, and deck screws, in various locations. All my lumber was planed for a true flat edge and ripped on table saw, homecenter lumber sucks. Heres a couple pics. The center support I have can pop out to slide a 75 gallon tank in from the front, but I used 2 40 gallon tanks instead and drilled them and siliconed them together with bulks. 75 was too tall to clean skimmer cup.
The tank is a 6' long 210. It has (2) 40 gallon tanks under it. The stand is solid, filled for years. I cheated though. I added extra silicone to all seams. I smeared over a full tube (of "GE silicone I" from home center) all over the bottom (it's covered in gravel, no one can ever see it) and taped the side corners and doubled up overlapping factory seams (used blue tape to pull for nice corner seam appearance).