Is this a touring or static caravan? I would work out the time it takes and price accordingly.
When I clean my own I use wfp, a short ladder with ladder mitts for the roof and detergent. I found it is a bit like doing a polycarb conny roof. If it's green it takes more time than if done regularly.
When my caravan is on site the site owners will get their staff to give it a once over including roof for £45. It's an old caravan and I just pay them.
Solar panels - make sure they are switched off. Use rubber work gloves too.
In general terms I avoid these solar jobs (and no caravan jobs) - too much like hard work - long poles and heavy work if on anything higher than a bungalow ...