I usually take the machine to the local self car wash bay on the way home from a ride. The trailer is in the bay and the tow vehicle is sticking out of the bay. I wet the machine down to get all the dirt loose, then soap it all up, let it sit for a minute or two, then rinse it off.
I spray everything down, but I don't let high pressure hit the dash bits or the seats. You have to use your best judgement on what can be sprayed with pressure and what can't.
Takes about 10-15 minutes depending on how dirty the machine is, and it air dries on the way home :-)
Costs about $10 but the convenience and time savings is well worth it.
A side benefit is the trailer gets cleaned in the process.