Pressure washing is a possibility, but you need to be sure to foil wrap your important electrical components, disconnecting the battery, cover any intakes, etc. Use the lowest water pressure possible.
Personally, I'd spray down the bay with a mild degreaser (I like Optimum Power Clean 3:1 unless your really dirty, then use full strength but test an inconspicuous area first.) , and use some various size brushes to get into the nooks n crannies, cover the important stuff, and then use a low pressure stream of water to rinse the bay. After that, use a vinyl dressing (Aerospace 303 protectant is my fav) to shine up your plastics & hoses.
Just be careful, use common sense, and you should be ok.