I also have the Century Plastics 4x6v box, and it is very well made. I cut a hole in the top to attach the gas vent line.
Tim
2013 F-350 6.7L Diesel, Crew Cab, Shortbed, Andersen Ultimate 2
2017 Grand Design Reflection 29RS, 540 watts of solar, Magnum MS2812 inverter, Bogart Engineering TM-2025 and SC-2030, weBoost 4G-M cell booster