Welcome to the forum, Subfan...this is sure the right place to research Airstreams...lots of info and friendly folks to answer whatever questions you might have.
The smaller ASs have smaller fresh water and holding tanks capacities, of course, and the 16' Bambi has a common black+grey water tank, rather than separate ones, and I should point out that early ASs didn't have black water holding tanks...(I don't know for sure when they became standard...I'm sure that's dicussed here somewhere)...
The rain...oh yes, you can hear the rain pitter-patting away. It's rather nice.
Good luck with your research!