It's great to have the option of hot water esp in the winter. I have heard of windows cracking but it is rare, as long as you don't have the water too hot on really cold days you will be OK. I have the 9KW webasto heater fitted by pure freedom, although it's a good system, it was very expensive and your batteries take a big hit, they are also prone to coking up if used regularly in small bursts. I hardly use it in winter now as I bought 2 portable immersion heaters off ebay, total cost was about £30, I drop them in the tank overnight and in the morning I have a 650 litre tank of hot water, if you can get electricity to your van at home and you use a tank as opposed to containers I would highly recommend using these, it was Smudger on here that put a link up for them a while back, they were imported from China.