On our lineup of trunk mounted water tank we use the Beckson 4" deck plate to allow for easy access to the tank system. The clear lid allows you to see inside the water tank both to check the tank's level and to see if fluid is flowing or if there's an EMP pump issue.
An additional plus is that the Beckson water tank lid can be optioned with the lid key making installation and removal easier. Nothing sucks more than breaking your fingers at the track trying to torque off a lid someone else decided to set to 100 ft-lbs. The Beckson lid key solves that too-often seen water tank issue.
Beckson Part Number: DP40-B-C