Another possible mounting method would be to make some bolts out of set screws and lock nuts, with the set screw Allen wrench socket on the opposite end from the lock nut. These "bolts" would be put into the frame holes from above, and then the tank would be lifted into position. The hex socket in the end of the set screw could then be used to keep it from spinning while tightening the nut against the tank.
The trick would be getting the tank into position without bumping the bolts out of their holes. Boyd recommends placing rubber sheet between the tank and the frame. If the holes in the rubber sheet were cut on the smaller side, then the sheet could be pressed onto the bolts to help hold them in place while raising the tank. Another option would be to use push nuts like these to hold the bolts in place:
https://www.mcmaster.com/94800A813/