I can find no reference to the fact that the hose needs to be changed every 12 months. Where did you obtain this information as I would then expect it to be done at every service or if not notification that it needs to be changed. The material should not be perishing within a period of 12 months unless it was of inferior quality. I would hae thought that every 5 years would be more appropriate.
I have a black high pressure hose andI I think it is 1.5 metres in length as the bottle is outside the caravan so not sure about the 600 mm unless that is for low pressure hoses.