ardly:
Apart from some suggestions of adding flow meters (and pressure gauges which would not work), I don't think there have been any suggestions with invasive solutions.Replacing a magnetic gauge with a magnetic gauge that includes a hall effect sensor is non-invasive, does not modify the tank and cannot cause a gas leak.
For my money it is the best solution and would give reasonably accurate regular readings of consumption - but it is not my money
I was not saying anything was invasive or dangerous as such, I think that's what your post is trying to say ie 'in your view it is safe and non invasive'
What I and some others have put forward is that your view counts for nothing in the gas suppliers eyes or their insurance cover.
Hence I am saying that the way forward is to talk to them/the suppliers first. coz the regs will be the regs for the country, and there is no getting around them. not sure which country the OP's gas tank is in?
In the UK it's a criminal offence just to take the front screwed cover off a simple indoors gas boiler without the corgi certs. many will think that over kill, but a few years back I guy on BBC news was sent to prison when his home gas mod blew his house up and killed the three children living next door too...I tried to search the BBC page for it but it's so full of gas explosions I got bored reading page after page
https://www.bbc.co.uk/search?q=gas+explosion&sa_f=search-product&scope=#page=1
The point is it doesn't matter if you're using a Hall Sensor or measuring space particles coming through the tank at near the speed of light. if the supplier aint happy about homemade electricery near his/her tanker you wont need a gas gauge coz you wont have any. even if the gauge is made by NASA!