Excellent, and correct advice from Bailey. A pressure washer will be far too powerful for most caravans.
Caravans are not like cars. Most of the seals between panels are of mastic based materials, windows are plastic, and any nice lettering to brand the caravan is simply stuck on. Shall I go on?
Put it this wasy. there is NO WAY I would use a pressure washer on MY caravan. Nice soft water and lots of gentle TLC with a sponge. Then a good polish. It will last you years.