Thats a good question
Well, i have just bought another round hence acquiring the trafic and tucker system, and taken on another employee. I thought by trying the shower heater for the time being would be a cheaper option to get us through the winter, and if it is any good, maybe sticking with it. As people have been running with them for a few years, its been tried and tested, so thought i don't mind paying out £300.00 ish at the moment, its better than £3000.00.
It won't be the same as the webasto as it wont have the blower, timer and frost protection, but at least we will have hot water to work with.
On another note, if your looking at a webasto add on, water fed pole at grantham are the cheapest for a one man basic set up, unless you are going to install it yourself. But they can also add on the extras.