Hello teoman,
To get high volume of CNG at low pressure, look into Adsorbed Natural Gas. No, not "absorbed", specifically "adsorbed". Different phenomenon.
https://cenergysolutions.com/ has a fair bit on the tech.
Here's a commercial source of similar tech tanks, albeit not rated for road use (though they do state safe/rated to take around in a truck to get to a place to use them.)
cylinders