Ahh, that's a very good question Grant. This new heater does seem more efficient and the exhaust isn't quite as hot but still not something you'd want to stick your hand in. Initially the set up produced so much heat you could seriously fry an egg on the roof. So, I fitted the deflector shield and covered the inside of the roof with some of that space shuttle heat resistant material. Basically quilted tinfoil. This allows the heat to escape out of the front door. The roof is cold to the touch so it works. Now some of the larger heaters have a flue which could go out through the roof or even the side of the trailer. I couldn't do that for a few reasons not least it would have set fire to the roof tent. I never really run the burner for long periods; its not like I am trying to full a bathtub. I have used it to shower and with the shower head set to the fine spray (which is lovely) the water flow on full and the heater flame setting on half, I was able to complete my ablutions without melting the trailer. This new heater makes water so hit it's actually unusable for washing. I run that straight into the kettle so that it saves electricity to boil it for a cuppa.
One thing worth doing is mounting it so that there is some shock absorption. I don't think they respond well to being battered about. Mine is over the axle and mounted on rubber bobbins to isolate it a bit. Seems fine. Also, have a look at the Sureflow pumps. Those little diaphragm pumps are rubbish. Fit one of those bad boys and you won't look back. I'm thinking about teeing off the output again and putting an outside tap on the back of the trailer for filling buckets to wash the truck with.
If you mount it to a door, there is a chance that it might get slammed about a bit. I think I speak for everyone when we say we'd like some build pics Grant .....
