Hi RileyAnn,
I have used one of the cheap flow-through "Brush-on-a-Stick" jobs to clean the roof of the caravan, but never with the hose connected as as water gushes out and the hose drops off when horizontal. I don't use it on the acrylic windows/rooflights as I don't want to add additional marring to the soft surface. Therefore, I bought one of these:
Brush on a stick 2.0
In general I use whatever I have for the car, but I tend to buy detailer-oriented products. So I use a microfiber wash-mitt and last washed the caravan with AutoGlym bodywork shampoo.
I've not used Fenwicks products for caravan cleaning, so can't comment on them. But my advice would be to apply some wax of some kind. Polishes will remove a layer from a surface, while a wax will add them. I have used a specialist synthetic car wax, known as a ceramic coating, which has meant that the water beads on the surface of the caravan and rolls off. It doesn't prevent black streaks though!