Dave I've always used a truck wash like CT18 for areas that I can't really wash properly with a sponge because it strips the dirt off.
Some people find it a bit harsh but I've never had an issue.
I also like to give everything a real light silicon spray. Not because it makes the engine bay look brand new again (although I do like the new look) but because it makes cleaning it next time a lot easier.
I know this method is hated by some but it works for me.