I don’t know Nozzi’s fitting, but it is possible to buy a remote “gas contents indicator”. CAK Tanks used to sell one, but I’ve just had a very quick look on their site and I can’t spot it. Maybe give them a call if that is what you’re after. http://www.caktanks.co.uk/CAK_Gas.htm
If it’s just an indicator on the tank, mine came with a gauge already fitted on each tank. Again, maybe speak to CAK about this.
As Nozzi’s is an “under-van” tank (of a type also sold by CAK), I can’t comment on how his set-up would relate to what you’re looking for, Pete. If you’re looking for a gas tank(s) to be fitted, there are two main (and there are others) tank fitters I know of – GasIt and LeisureGas. They can advise you.
Good luck.
Barry