i love the fear people have, like water never gets in the bay when you hit a puddle or drive through a weir etc.
there is no issue with jet washing the bay if your sensible, avoid the key areas such as spark plugs/dizy/coil etc etc. its al designed to be water resistant anyway so can take water no issue, and if the jetwash isnt aimed directly at the connections its absolutely fine, never had an issue and i have jetwashed the bay in every car i've owned over the past 10 years and never ever broken anything. you just get the dodgy water in a sensor idle for 5 mins or so until it dries out, then its fine.
in other words, man up if you want a clean bay