I'm a bit surprised about the negative attitudes to gas califonts, while I have no experience with a mobile installation, I grew up with a small gas califont in the family home's bathroom and have since used them in restaurant kitchens where continuous hot water was a necessity.
Even with the smallest ones I've never experienced any water temp issues despite being in high demand situation. Indeed most califonts have no problem heating water to at least the international OH&S standard for shower or bath temp of 27C to 34C.
After reading this thread tonight I called a restauranteer mate who operates a largish restaurant, his attitude was that if you need continuous high temp water then the only option was a gas califont (his restaurant kitchen has 2 Bosch units, one supplies the washing up sinks, the other supplies the dishwashers).
Of course I would concede the noise could be a little irritating in a small enclosed area such as a motorhome or caravan.
There is a major difference when it comes to usage of "hot water on demand systems" and "storage systems", with "on demand systems" you set the temp so that you only require a small amount of cold water added, whereas with storage systems it is recommended that the water is stored at 70C or more to avoid the growth of bacteria such as legionella.
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