Doesn't the webasto heat your coolant cirulate it around the engine and then blow it into the cab?
Fitting No problem but I have zero time I have sooo much on. Might be worth you bringing it down and fitting it when I'm working on the trialer that way if y ou need owt we can sort it.
Some of the svo guys run a fuel pre heater for cold weather. Its similar to a glow plug in a small reservoir of fuel and heats it up.