I really sympathize with those of you still in school, especially those living on-campus.
For undercarriages, I use my undercar wand for quick rinses but to really get things clean I jack it up (don't forget the jackstands...[stuff] happens) and clean with brushes/mitts/etc. Clean it up *really* well once and then it's easy to keep it that way.
Engine compartments seem to stay pretty clean once you do the initial, big cleanup. I don't dress things under the hood on my drivers, I just *clean* them a little bit at every wash, primarily with small BHBs aqnd regular shampoo mix. I towel-dry things under there as best I can, using a bit of QD to add a little sheen. But just like the undercarriage, the big thing is to clean it up *really well* one time. Get rid of all the grime and oxidation (alternator cases seem to always oxidize) and then the routine cleanups will only take a few minutes.