Hi Rich,
Open up the machine and do visual checks on all of the wiring. Look out for any wires that a barem loose spade connectors. Check the main flex cable & plugs. Check that all hoses are clamped on nice & tight. Check that the water pump & vac motors are secured to the unit. Check the brushes on each vac motor. vacuum out any dust inside that houses all the internal parts. Make sure cooling fans are working ok & are free from dust. Personally i would do all these checks every month. I would also carry a spare vacuum motor & water pump on the van along with a basic tool kit that you would need to carry out any repairs whilst on site. Incluse in the tool kit a volt meter, PTFE tape and spade connectors.
Richie.