Peter,
I do not think you should be alarmed unduly. Without implying any disrespect to Parksy, I do feel his opinion is a bit of scaremongering. Thetford fridges were originally the Norcold Company of the US and were taken over by Thetford to get entry to that particular market. Their fridges have been supplied in many countries throughout the world, and I note even the latest brocure from Thetford indicates full approval for the Australian market among others.
Yes, there have been reported problems particularly with a batch of electronic panels supplied around 2005, but there have also been various problems with Dometic/Electrolux fridges over the years. In many cases these were traced to poor installation by the manufacturer and that is where I feel anyone with a fridge problem, should start. I also wish to correct my earlier comment on flues with Thetford fridges. I now note they do have flues although they exhaust immediately behind the vent, not through it as with Dometic, so that threw me. But have a look and it should be there. There should also be a vent in the floor at the rear next to the gas burner to allow gas to escape in the event of a leak.
I cannot comment on Parksy's comment on repeated burner changes as I usually use electric operation. I have had 2 Thetford fridges to date and so far, touch wood, have not seen any problem. Yes, the burners should be checked annually, and cleaned if required but that is due to a EU Directive covering ALL gas equipment, not just Thetford. In fact I would suggest that as far as cooling efficiency is concerned Thetford beats Dometic especially in the very hot Med. However, that again could be down to installation. I had a Dometic in my Compass motorhome and it was very poor in heat. I eventually found that Compass had not fitted any of the baffle plates at the back. So, if you can see daylight around the fridge, or feel a draught, then check that part out.
I am not trying to jump on any 'hobbyhorse' regarding Thetford but would state that this is a long time manufacturer of units in both the European and US markets, as well as others, and so have as good reputation as anyone else.