Speakers and amp suggestions for motorcycle?

My brother-in-law asked me about speakers for his Harley (not sure which year or model). The faring has two stowage compartments, and he said that Harley sells a speaker kit that utilizes those compartments ...and asked me if I thought such a kit might be any good (or barring that, what else I might recommend). He plans to use his iPod as the source, and he knows that he'll need an amp (or perhaps an amp comes with the Harley kit).

While I have no direct experience with motorcycle stereo (and would therefore have no idea if the Harley kit might be any good), I did make it clear that, for a number of reasons, bass response (presumably from any pair of five or six inch coaxials or the like) would be nil ...that, at speed, SQ would be sort of an oxymoron ...that those faring compartments might be susceptible to resonance (and might need treatment of some kind) ...that, apart from a Harley kit (which would presumably be built to handle the elements) he would need "marine" rated speakers ...and that there are amplifiers specifically designed for motorcycles and the like.

Bear in mind that he's not an audiophile, and has modest expectations. His bike is not overly loud; and he's not looking to blare tunes, but rather just a bit of unobtrusive accompaniment (i.e. so as not to drown out anything going on around him).

While he's not looking to throw a bunch of money at it, he doesn't want to waste his money on a bunch of garbage.

Any questions/thoughts/suggestions would be greatly appreciated!