Have you seen ELF? hard to describe... best to check it out at http://www.organictransit.com/features/ add door panels and fenders for the two front wheel and you should stay bit more dry.

It's too pedantic for me but uber practical. They are setting up a distribution center in Portland Or is last I heard. Dutch cargo bike is very practical. I wish more people would consider it.

And yes, I've seen lot of Xtracycles around town (Portland). I've even seen a specially built bike with a keg and taps... not sure how legal that is.