Hello Ian, I personnally would NOT recomend using a pressure washer on your caravan the reasoning behind it being
The seals around the caravan panels are basicaly mastic and the power of a pressure washer (in my limited experience ) will remove the mastic and allow the ingress of water. The door seal may let in water and do the same thing only letting the water into the caravan itself. I had a caravan myself that had been washed with a pressure washer and it fetched the mastic out of the joints around the panels, and the sky lights too. The graphics were a problem aswell as it had got behind them and they eventually came off . We were very dissapointed as the caravan was so nice and had everything but alas. It caused me loads of problems and work to reseal it, and to be honest I got rid of the caravan.