i have weighed the 2 coin ops I have owned...I used water the first time, but it in bags, in bags, in bags and it worked out fine and at 8 lbs per gallon it seemed like and okay option...this time i used gallon milk jugs which I don't recommend unless you are going to bag, bag, bag them because mine leaked this time...slow but
anyway, water is a bad option all things said...sand is a cheap, fairly dense and safe alternative and you can create bags to the shape you want
however, the best thing I have found, but is anything but cheap, is lead shot (used to fill shot gun shells)...25 pound bag is about $30-$35
however, they are small and really dense of course and you can put them on the railing on the sides, one by each leg (at least). I don't think you are going to have issues with the bottom warping but this removes that as being an issue
right now, i have only 2, one on each end, but if I had the funds, I would have 8 and add 200 lbs
if i was designing a table, it would have 6 inch square legs made of steal with a black powder coat on the exterior...plate on the bottom would be welded...the screw for the foot would be 1 inch thick, and the plate on the bottom would have threading already in the center but there would be another plate about 3 inches in which was welded to the inside and had the same threading so that the screw threads in two places helping with stability
there would be a third plate, a couple inches above the second, which would be the “floor”…the legs would be hollow and you would add sand or lead, your choice, as much as you wanted the weight to be…this way, the legs if fully filled with lead, could easily weigh 150 lbs each
the legs would travel as far up into the cabinet as possible…with all these features the stability of the table would be unequaled…add to that a two inch thick playfield and we could revolutionize the game…I want the table so that people can play as aggressive as they want without concern of jarring and if you jarred on this table, at 800 lbs, you would have really deserved the call
I want the goalie defending the 3 bar, to be as crazy, fast, jerky as they want without concerning themselves with resets
Anyway, short answers…”Sand” (50 lb bag about $5) and “No”