On ANY electronic engine, I would not use a pressure washer-- just too many electrical connections. Sure, most are water-RESISTANT. Water-resistant does not necessarily mean water-proof to high PSI pressure washers.
Safest is to buy a can of WD-40 and a roll of paper towels and clean it by hand. Also a good opportunity to check over hoses, belts, etc.
And, more important with a rear radiator (if that is what your coach has) is cleaning the FRONT of the CAC(Charge Air Cooler). Most CAC's are aluminum, so an aluminum-friendly degreaser is highly recommended.
Simple Green EXTREME fits that description-- it was developed for degreasing aluminum aircraft. One gallon should last you the life of the coach.