We usually just wash our Seneca where it is parked, we have a telescopic soft brush that connects to the hose on the pole. I've had it 20 years, and have not found another that has bristles on the brush as soft as what this one has. There is no way in #%&@ that I am going to get on that roof when it is wet, Winter is coming and the snow cleans up everything eventually.
We also have a 6' pole with a spring loaded pin that works with most of the commercial window washing tools. A window washing kit that has the microfiber wash head works pretty good when used with a plain terry-cloth towel instead (https://a.co/d/3cI8ql7
We then use a second pole with a dry towel on it to dry the upper portion of the Seneca.
We have been to Blue Beacon Truck Washes a couple of times. Costs between $40-$60 a wash and they use high pressure sprayers and hand brushes on poles. Use them with caution as they don't take the care they should around the fridge, water-heater and vents that they should.