Boss Ross, here are a few things to check.

As others have stated makes sure the screws are tight enough to just press the tank to the O-rings. It should be able to wiggle a little. The O-rings should not be compressed to the point they bulge. Be sure to use the m3 washer between the tank and screw head.

Check the drip tube from the tank and trim the tube so it ends just before going into the mud guard. You do not want the drip tube going into the mud guard. This can cause the tank to break when flexing.

Check clearance around the tank. It should not touch anything (i.e. the front chassis brace, drive line, pipe) and should be free to vibrate and slightly move. There should be about 5mm of clearance between the pipe and tank. You might need to reposition the pipe, tank or fuel line if it is too close. Make sure the pipe is pushed as far down and to the left of the car as possible. The mud guard should be touching the pipe on the bottom and left sides. I test this by flexing the mud guard up and the pipe should move too.

Make sure the pipe hanger is not touching the tank on the bottom side. The hanger should not protrude through the right side of the hanger block. Also make sure the hanger block is extremely tight. Be sure to use Loctite on both the m5 set screw and the m4 flat head screw in the hanger block.