Thank-you for the replies, it gives me an idea what to charge.
None of the caravans on the site have gutters, they look similar to the one in the attached picture.
I have been cleaning a lot of FSG and conservatory roofs this week and I do apply TFR first, I actually find it easier and quicker to apply the TFR with a hand brush from a bucket and then WFP to rinse off.
Smudger, if you don't WFP caravans anymore, what do you use, a pressure washer?