I did the top side of mine about a couple months ago at a local car wash.
I used plastic bags and duct tape on the coil pack and the spark plug wire ends and also plastic bagged the area by the alternator (couldn't get to it without the front end off so just tried to cover area around it). I sprayed everything with gunk engine degreaser and rinsed most areas then used the pressure washer setting on the car wash hose for dirty areas that weren't near any sensors. Just try your best to not hit any sensors but if they get a little wet it's not that bad. After all anything on the bottom of the car would get wet from rain anyways so just watch the alternator coilpack and plug wires IMO